Negative Metastatic Breast Cancer Research Articles

Abstract OT3-07-01: Real-World Data on First-line Treatment of HR-positive, HER2-negative, Metastatic Breast Cancer in Brazil (BRAVE Study/LACOG 0221)

Abstract Background: It is estimated that 50 thousand patients live with metastatic breast cancer (MBC) in Brazil. A recent Brazilian registry (LACOG 0312) on MBC demonstrated a median overall survival (OS) by breast subtype of 15 months for triple negative, 23 months for HER2 positive, and 42 months for Luminal tumors, which are very similar to developed countries except the HER2 positive group which have limited access to targeted agents in the public health system. Recently, CDK 4/6 inhibitors were approved for the treatment of HR+ HER2-negative MBC with an improvement in progression-free survival (PFS) and ribociclib and abemaciclib demonstrating benefit in OS over endocrine therapy alone, establishing the standard of care in first-line setting for this BC subtype. In Brazil, disparities exist in the incorporation of novel anticancer agents between public and private health systems limiting treatment options for patients with HR+ HER2- negative MBC in the public system, which covers most of the population. The BRAVE study aims to describe the patient journey and current patterns of care for HR+ HER2-negative MBC to identify possible gaps and how health insurance type influences treatment patterns in Brazil. Trial Design: This is an observational, retrospective cohort study. All patients diagnosed with mBC (either de novo or recurrent) in the period of January 2018 to December 2020 at participating centers will be included. Data will be collected from medical records. No interventions are proposed. Enrollment of a total of 300 patients (150 patients from public health care system and 150 patients from private health care system) is planned. ClinicalTrials.gov identifier: NCT05034393. Eligibility: Inclusion criteria: women ≥18 years old; histologically confirmed HR-positive HER2-negative invasive breast cancer; HR-positive, defined as 1% to 100% of tumor nuclei positive for ER and/or PgR as per ASCO/CAP Guideline 2020 or Allred score of ≥3; HER2-negative, defined as IHC result is 0/1+ or 2+ with ISH negative as per ASCO/CAP Guideline 2018; diagnosed with de novo or recurrent metastatic breast cancer between January 2018 and December 2020. Exclusion criteria: male BC; first-line treatment for mBC received through clinical trial. Specific Aims: Primary objective is to describe the first-line (1L) treatment of HR-positive, HER2-negative mBC in Brazil. Secondary objectives are to describe progression-free survival (PFS) in the 1L setting until month 24; describe and compare the 1L treatment of HR-positive, HER2-negative mBC and PFS until month 24 according to the health care coverage (public vs. private); describe timelines from symptoms, histopathological diagnosis, molecular test, and treatment; describe the mBC pathological characterization; describe frequency of diagnostic tests to define breast cancer molecular subtypes; describe the subsequent line of treatment and corresponding PFS; describe overall survival (OS); evaluate PFS and OS according to visceral vs. non-visceral metastatic disease, primary endocrine resistance vs. acquired endocrine resistance, de novo versus recurrent disease, public vs. private health system and pre vs postmenopausal status. Statistical Methods: No a priori sample size calculation was performed. The expected sample size of 150 patients in each group allows description of the proportion of patients using CDK 4/6 inhibitors with two-sided 90% confidence interval ranging from 53.4% to 66.6% when the expected proportion is 60% in the private health system. Present Accrual and Target Accrual: A total of 12 sites of 14 planned were activated. The first patient was enrolled on February 8, 2022. As of June 24, 2022, a total of 122 patients were enrolled, 86 from public and 36 from private health system. The target accrual of 300 patients is expected to be completed by November 2022. Results are expected to be presented by April 2023. Funding: Novartis. Acknowledgements: SAS. Citation Format: Gustavo Werutsky, Tomás Reinert, Daniela D. Rosa, Romualdo Barroso-Sousa, Heloísa Resende, Poliana A. Signorini, Juliana G. Martins Fagundes, Jose Marcio B. Figueiredo, Eduardo Cronemberger, Aline C. Vieira, Jorge Henrique Santos Leal, Luiza Nardin Weis, Ludmila Thommen, Rafaela G. Jesus, Gustavo Gössling, José Bines. Real-World Data on First-line Treatment of HR-positive, HER2-negative, Metastatic Breast Cancer in Brazil (BRAVE Study/LACOG 0221) [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr OT3-07-01.

Abstract P3-05-10: Disease features, genomic profiles and outcomes of younger vs. older Chinese hormone receptor positive (HR+), HER2 negative (HER2-) metastatic breast cancer (MBC) patients

Abstract Background: Breast cancer in younger women has been characterized as a more aggressive disease with relatively poor outcomes compared to breast cancer in older women. This pattern has been attributed to a variety of clinicopathologic characteristics including the enrichment of aggressive HER2+ and TNBC subtypes in younger patients. However, similar to older breast cancer patients, the majority of young breast cancer patients are HR+/HER2-. Here we have evaluated the clinicopathologic characteristics and genomic profiles of real-world HR+/HER2- MBC patients to examine the determinants of outcome for younger vs. older patients in this subtype. Patients and Methods: This study included 65 Chinese patients presenting with HR+/HER2- MBC at the Peking University Cancer Hospital. Blood samples were collected upon metastatic disease diagnosis before treatment and profiled with the targeted 152-gene PredicineCARETM sequencing panel. Fourteen patients were < 40 years, 19 were 40-50 years, and 32 were > 50 years at the time of primary cancer diagnosis. Kaplan-Meier survival analysis was performed to analyze outcomes including overall survival (OS), disease free survival (DFS) and progression free survival (PFS) in association with clinicopathologic and genomic variables. OS was also evaluated in association with age in separate multivariate models using Cox proportional hazards regression. Results: Significant variation across age groups was observed for several clinicopathological features, including molecular subtype classification (p = 0.045), de novo Stage IV disease (p = 0.011), type of adjuvant endocrine therapy (p = 5.56E-06), resistance to adjuvant endocrine therapy (p = 0.015) and receipt of adjuvant chemotherapy (p = 0.042). Luminal B status was most frequent in patients < 40 years (92.31%), whereas de novo Stage IV disease was more prevalent in patients > 50 years (37.5%). Aromatase inhibitors (AIs) were administered as adjuvant endocrine therapy (ET) to 73.68% of women > 50 years vs. 16.67% and 0% of women aged 40-50 years and < 40 years, respectively. Resistance to adjuvant ET was observed in 23.08% of patients < 40 years but was not observed in the other age groups. Adjuvant chemotherapy was received by a higher proportion of patients in the 40-50 year age group (94.44%) compared to patients < 40 years (69.23%) and patients > 50 years (60%). No differences in somatic gene alteration frequencies were observed across age groups, menopausal status, germline mutation status or tumor grade. However, a higher frequency of FGFR1 alterations was observed in patients classified as Luminal B vs. A (p = 0.048). Comparison of profiles across women who received adjuvant ET revealed a higher prevalence of FGFR1 (p = 0.012), ATM (p = 0.047) and CCND2 (p = 0.04) alterations in patients treated with AIs vs. SERMS. In addition, a higher frequency of APC alterations was observed in patients with high (≥ 20%) vs. low (< 20%) Ki67 index (p = 0.035). At the univariate level OS was significantly associated with age (p = 0.039). OS was shortest in patients > 50 years, intermediate in patients < 40 years, and longest in patients 40-50 years. Across all patients, shorter OS was also associated with de novo Stage IV disease (p = 0.0001), Luminal B subtype (p = 0.008), adjuvant ET with AIs vs SERMS (p = 0.028) and the presence of an FGFR1 (p = 0.028) or CCND2 (p = 0.033) alteration. In multivariate analyses, OS remained significantly longer for patients aged 40-50 years after adjustment for de novo Stage IV disease, Luminal B subtype and FGFR1 status (all p < 0.05). Conclusions: In this group of real-world HR+/HER2- MBC breast cancer patients, younger age was not associated with worse outcomes. While current guidelines recommend treatment decisions based on tumor biology rather than age, young HR+ breast cancer patients are more likely to receive chemotherapy. Our findings support the development of biomarker-driven treatment strategies for these patients. Citation Format: Jinhao Wang, Yaxin Liu, Bin Shao, Hang Dong, Tiantian Zheng, Pan Du, Shidong Jia, Bonnie King, Jing Wang, Xiaoran Liu, Huiping Li. Disease features, genomic profiles and outcomes of younger vs. older Chinese hormone receptor positive (HR+), HER2 negative (HER2-) metastatic breast cancer (MBC) patients [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P3-05-10.

Abstract P4-01-41: Clinical outcome and toxicity profile of Cyclin-dependent kinase 4/6 inhibitors in combination with hormonal treatment in management of metastatic breast cancer patients: A Middle-East Real World Experience

Abstract Background: Cyclin-dependent kinase 4/6 (CDK4/6) inhibitors in combination with hormonal treatment is the standard of care in the management of hormone receptor positive, human epidermal growth factor receptor-2 (Her2) negative metastatic breast cancer (MBC) patients. Data coming from the Middle east region is very rare and our patients’ population were poorly represented in the CDK4/6 inhibitors landmark clinical trials, This retrospective study is to evaluate our real-world experience with this treatment combination in our patients’ population. Patients and methods: A retrospective study was conducted in a middle eastern tertiary institution, where the clinical data of treatment outcome and toxicity were collected from the electronic medical records of 164 patients with hormone receptor positive, Her2 negative MBC who were managed with CDK4/6 inhibitors in combination with hormonal treatment, at and beyond first line of treatment. Progression free survival (PFS) was the study primary objective, Objective response rate (OR), Overall survival (OS), and toxicity profile were the secondary objectives. Results: From January 2017 to April 2021, 164 patients (5 men and 159 women) were managed with CDK4/6 inhibitors in combination with hormonal treatment for MBC, median age was 52 years (IQR: 45-59), 63% of patients were postmenopausal, 60% had luminal type B tumors, 22% had Her2 expression of 2+ by IHC, 55% had de Novo metastases, 67% had visceral metastases, 61% defined to have endocrine resistant disease (13% primary and 48% secondary resistance), CDK inhibitors (46% Palbociclib, 54% Ribociclib) were given as 1st, 2nd and beyond 2nd line in (48%, 28% and 24% respectively), at a median duration of follow up of 25.3 months (IQR: 13.8-33.9 months), the median PFS for the overall group was 14.2 months (CI 09.8-18.7), it was highest for 1st line treatment 19 months vs 15 and 5 months for the 2nd and beyond 2nd line treatment respectively. The median overall survival was 51.6 months (CI 35.8-67.5) for the whole group, 50.3 and 51.6 months for 1st and 2nd line vs 33.1 months for beyond 2nd line treatment. 5% of patients had achieved complete response, 37% partial response, and 24% had stable disease, with a clinical benefit rate of 74%. A body mass index (BMI) < 30, KI67 < 20%, luminal type A, de Novo metastases, Ribociclib as a CDKi, Aromatase inhibitor (AI) as the hormonal partner, and introducing the treatment combination in early treatment lines (1st and 2nd lines) were all associated with significantly higher PFS in univariate analysis. BMI and AI were the only factors associated with significantly higher PFS in multivariate analysis. Efficacy was consistent regardless of the menopausal status, type of endocrine resistance, and site of metastases. The most common toxicities were neutropenia, fatigue, vomiting, diarrhea, QTC prolongation and hepatic toxicity, the most common G3&4 toxicity were Neutropenia 56%, hepatic toxicity 5.4% and QTC prolongation in 4.3%. Treatment was permanently stopped because of toxicity in 12 patients (7.3%). Conclusion: Our real-life data came consistent with the pivotal clinical trials’ results, encouraging and supporting the use of CDK 4/6 inhibitors in combination with hormonal treatment in our patient population with metastatic breast cancer, especially in the early treatment lines, deferring the start of more toxic therapies to a later stage. Citation Format: Ahmed Mostafa Gad, Adhar AlSayed, Aisha AlShibani, Taher Twegieri, Kausar Suleman, Dahish Ajarim. Clinical outcome and toxicity profile of Cyclin-dependent kinase 4/6 inhibitors in combination with hormonal treatment in management of metastatic breast cancer patients: A Middle-East Real World Experience. [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P4-01-41.

Abstract OT2-01-01: Trial in Progress: Clinical Utility of Fluoroestradiol F18 PET/CT in Metastatic Breast Cancer Patients with ER-Positive and HER2-Negative Primary Lesions after Progression on First Line Hormonal Therapy

Abstract BACKGROUND: Cyclin-dependent kinase 4/6 (CDK4/6) inhibitors combined with endocrine therapy are the recommended first-line standard-of-care (SOC) treatment for estrogen receptor (ER)-positive, human epidermal growth factor receptor 2 (HER2)-negative metastatic breast cancer (MBC) patients. After progression on first-line treatment, current clinical practice guidelines (NCCN, ESMO) recommend to sequence endocrine therapy (in absence of visceral crisis) until there is no clinical benefit after up to 3 regimens, and subsequently initiate chemotherapy regimens. However, clinical benefit for endocrine monotherapy after progression on first-line standard-of-care is limited, with median progression-free survival (PFS) of 2-5 months. Multiple factors can contribute to endocrine therapy resistance, including changes in ER expression, (epi)genetic mutations, and/or clonal selection under therapeutic pressure. ER heterogeneity can occur over time (temporal) as well as between lesions in a patient (spatial). As confirmed by tissue biopsy, greater than 20% of MBC patients have discordance in ER expression between their primary tumor and a metastatic lesion. Measuring total ER heterogeneity in a patient – the variation in ER expression at whole body level across all MBC lesions – is not clinically feasible by tissue biopsy alone. Fluoroestradiol F18 (Cerianna), also called 18F-FES, is a radioactive diagnostic agent that can be used with PET/CT for in vivo detection of ER-positive lesions in MBC with high accuracy. Results from 18F-FES PET/CT studies have shown that ER expression across MBC lesions at whole body level is heterogeneous in approximately half of ER-positive, HER2-negative MBC patients. In this study, we aim to evaluate the clinical utility of 18F-FES PET/CT to guide second-line treatment decision in ER-positive, HER2-negative MBC patients with progressive disease on first-line SOC hormonal therapy. METHODS: Fluoroestradiol F18 (Cerianna) is being evaluated in a phase 4, open-label, prospective cohort study enrolling 206 patients at 20-30 centers in the United States. Patients diagnosed with ER-positive, HER2-negative MBC who have progressive disease on first-line aromatase inhibitor therapy with or without CDK4/6 inhibitor will be included in the study; patients with isolated hepatic metastases will be excluded. All patients will undergo an 18F-FES PET/CT scan. The treating physician will complete a standardized questionnaire to indicate the second-line therapeutic management plan before the scheduled 18F-FES PET/CT. After interpretation of 18F-FES PET/CT by local radiologist or nuclear medicine physician, imaging results will be provided to the treating physician who will then fill out a similar questionnaire to specify the final therapeutic decision. The proportion of patients with a change in therapeutic management plan based on incorporation of 18F-FES PET/CT results will be the primary endpoint. During the study follow-up period of 18 months, data on SOC imaging, treatments/procedures received, and clinical outcomes will be collected. Secondary endpoints include visual and quantitative heterogeneity assessment of tumor 18F-FES uptake, and PFS rates at 6 months and 18 months after 18F-FES PET/CT, which will be assessed between patients with and without a change in therapeutic management plan. The trial is planned to begin enrollment in Q3 2022. Clinical trial information: NCT05068726 Citation Format: Stephanie van de Ven, Feng Luo, Nicholas DiGregorio, Adolfo Fuentes-Alburo, Francois Tranquart. Trial in Progress: Clinical Utility of Fluoroestradiol F18 PET/CT in Metastatic Breast Cancer Patients with ER-Positive and HER2-Negative Primary Lesions after Progression on First Line Hormonal Therapy [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr OT2-01-01.

Abstract P5-02-49: Efficacy of subsequent-abemaciclib treatment after disease progression on palbociclib combined with endocrine therapy in patients with ER-positive HER2-negative metastatic breast cancer

Abstract Purpose: Currently, CDK4/6i combined with endocrine therapy (ET) has become the standard of care as first- or second-line treatment for estrogen receptor-positive (ER+) human epidermal growth factor receptor 2-negative (HER2-) metastatic breast cancer (MBC). However, at present, there are no guidelines for the selection of appropriate treatments after disease progression on prior CDK4/6i treatment combined with ET. Therefore, this retrospective study aimed to verify the efficacy and evaluate predictive factors of clinical outcomes in the patients with ER+/HER2- MBC during subsequent-abemaciclib treatment after disease progression on prior-palbociclib combined with ET. Methods: In total, 81 patients with ER+/HER2- MBC were treated with palbociclib and ET at our medical center between December 2017 and November 2020. Among them, 25 patients who received subsequent-abemaciclib after disease progression on prior-palbociclib were included. All patients provided informed consent for the indicated treatment. Clinicopathological variables were compared using Fisher’s exact test. The Mann–Whitney U test was used to compare categorical variables. PFS and time to chemotherapy (TTC) were estimated using Kaplan–Meier analysis with 95%CIs. Results: The median age was 69 years, and four women were premenopausal. Stage IV disease occurred in 28.0% (7/25) and visceral metastases were observed in 68.0% (17/25) of the patients. The treatment line of prior-palbociclib was the first-line in 3 (12.0%), second-line in 11 (44.0%), and third- and late-line in 11 patients (44.0%). The median PFS of prior-palbociclib plus ET was 6.3 months (95%CI=5.814–6.786). Subsequent-abemaciclib combined with fulvestrant after disease progression on prior-palbociclib was administered in 64.0% (16/25) of the patients. Median numbers of previous ET and chemotherapy of subsequent-abemaciclib were 2 and 0, respectively. Subsequent-abemaciclib after disease progression on prior-palbociclib resulted in an ORR and clinical benefit rate (CBR) of 16.0% (4/25) and 44.0% (11/25), respectively (Table 1). Kaplan–Meier curve analysis showed that the median PFS was 5.3 months (95%CI=3.082–7.518). Univariate analysis revealed that the best overall response (BOR) ≥PR and progression-free interval (PFI) ≥6 months in prior-palbociclib contributed to better clinical outcomes. Moreover, in multivariate analysis, BOR to prior-palbociclib was the only independent predictive factor for PFS (HR=0.190; 95%CI=0.050–0.722; p=0.015) (Table 2). With regard to grade ≥3 TRAEs in the subsequent-abemaciclib, neutropenia and diarrhea were observed in 16.0% (4/25); appetite loss and fatigue in 12.0% (3/25); leukopenia and anemia in 8.0% (2/25); and thrombocytopenia and liver dysfunction in 4.0% (1/25) of patients. Twelve patients (48.0%) required dose reduction due to TRAEs grade ≥3 in subsequent-abemaciclib. Of them, 10 patients required one dose-level reduction and 2 needed two dose-level reductions. Three patients (12.0%) required dose discontinuation: two had uncontrollable appetite loss and nausea and one had pneumonia. Of the 25 patients, 12 were not administered any prior chemotherapy and the median TTC in those treated with subsequent-abemaciclib was 33.9 months (95%CI=11.334–56.136). Next-line treatment after disease progression on subsequent-abemaciclib in the patients who were not administered prior chemotherapy was performed in 2 (8.0%) who were treated with ET and in 12 (48.0%) who were treated with chemotherapy (1 taxane-based, 7 eribulin, and 4 oral 5-fluorouracil). The median PFS in patients treated with chemotherapy after disease progression on subsequent-abemaciclib treatment was 6.2 months (95%CI=3.484–8.916). Table 1. Best overall response rate in patients with ER+/HER- MBC who were treated with subsequent-abemaciclib after disease progression on prior-palbociclib Table 2. Univariate and multivariate analyses of the progression-free survival in patients with ER+/HER2- MBC treated with subsequent-abemaciclib after progression on prior-palbociclib Citation Format: Hirohito Seki, Taketo Nakai, Ken Shimizu. Efficacy of subsequent-abemaciclib treatment after disease progression on palbociclib combined with endocrine therapy in patients with ER-positive HER2-negative metastatic breast cancer [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P5-02-49.

Abstract P4-07-09: Identifying Drivers of First-Line HR+/HER2- Metastatic Breast Cancer Treatment Choices

Abstract Background: Despite demonstrated clinical benefits of first line (1L) cyclin-dependent kinases 4/6 inhibitors (CDK4/6i) and their preferred status in the NCCN guidelines, many appropriate patients with hormone receptor positive (HR+)/human epidermal growth factor receptor 2 negative (HER2-) metastatic breast cancer (mBC) in the United States (US) may still receive chemotherapy or endocrine monotherapy. US oncologists may consider treatment expectations, patient clinical characteristics, and non-clinical factors (e.g., cost, anticipated adherence) when selecting 1L mBC treatment regimens. However, little is known about how prevalent these decision factors are among US oncologists. Comprehensively understanding the decision-making process in 1L treatment selection is a critical step towards ensuring equitable care for patients with HR+/HER2- mBC. Objective: To describe self-reported clinical and non-clinical factors considered by US oncologists in selection of 1L treatment for HR+/HER2- mBC. Methods: Data were collected through from an anonymous cross-sectional online survey from a convenience sample of US oncologists from August-October 2021. Eligible oncologists were board certified, in practice 2-30 years, ≥50% of time spent in direct patient care, and managed ≥5 1L patients with HR+/HER2- mBC in past 3 months. Respondents were sampled from a national research database of physicians sourced from multiple databases (e.g., American Medical Association Physician Masterfile). The survey captured self-reported demographic and practice characteristics and reported importance of the following factors in selecting 1L treatment for patients with HR+/HER2-mBC: anticipated treatment efficacy and safety, patient demographics, and clinical and non-clinical characteristics. Study variables were summarized via descriptive statistics. Correlation analyses evaluated associations between patient demographics, clinical characteristics, treatment expectations, and non-clinical characteristics and oncologists’ self-reported 1L prescribing rates of CDK4/6i, aromatase inhibitor (AI) monotherapy, and chemotherapy. Results: 250 oncologists participated; 67% from community practice and the remainder from academic institutions (Table 1). Anticipated treatment efficacy and safety/tolerability were ranked as the most important factor considered by oncologists when selecting 1L treatments. 1L CDK4/6i prescribing was most strongly correlated with patient Medicare eligibility (r, 0.54, p< 0.05) and postmenopausal status (r, 0.67, p< 0.05). 1L chemotherapy prescribing was most strongly correlated with patient premenopausal status (r, 0.42, p< 0.05) and perimenopausal status (r, 0.31, p< 0.05), and physician consideration for patient symptom burden (r, 0.31, p< 0.05). 1L AI monotherapy prescribing was most strongly correlated with concerns with expected patient compliance to treatment (r, 0.42, p< 0.05) and patient cost/logistical challenges (r, 0.41, p< 0.05). Conclusion: This study found a variety of patient, clinical, and non-clinical factors may underlie US oncologists’ selection of 1L treatment for HR+/HER2- mBC. Anticipated efficacy and safety/tolerability were reported as the most important factors in 1L treatment decisions. Patient demographics, clinical characteristics, and considerations for cost and compliance challenges varied in association with 1L CDK4/6i, chemotherapy, and AI monotherapy prescribing patterns among US oncologists. Table 1. Oncologist Demographic and Practice Characteristics Citation Format: Adam M. Brufsky, Martine C. Maculaitis, Lewis Kopenhafer, Patrick Olsen, Ashley S. Cha, Lillian Shahied Arruda, Wendy Heck, Samantha K. Kurosky. Identifying Drivers of First-Line HR+/HER2- Metastatic Breast Cancer Treatment Choices [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P4-07-09.

Abstract P5-02-50: Do thymidine kinase 1 (TK1) plasma concentration and activity play a role in therapy management of metastatic breast cancer patients treated with CDK4/6 inhibitors?

Abstract Introduction: CDK4/6 is a checkpoint kinase, regulating the transition of the S into the G2 phase of the cell cycle. As a cell transverses through the cell cycle, thymidine kinase 1 (TK1) is expressed and represents a direct marker of proliferative activity.which might indicate therapy efficiency of CDK4/6 inhibitors (CDK4/6i), the first choice of therapy in case no sign of visceral crisis is detected in hormone receptor positive (HR+), HER2 negative (HER2-) metastatic breast cancer (MBC) patients. We here determined whether the activity and/or concentration of TK1 in plasma samples of MBC patients treated with CDK4/6i harbours predictive, monitoring or prognostic value. Methods: Blood of 90 HR+/HER2-MBC patients drawn at baseline of CDK4/6i (Ribociclib/Palbociclib) plus endocrine treatment and 18 HR+/HER2-MBC patients drawn before initiation of endocrine monotherapy (control), as well as available matched blood samples of these patients after six months under TX (n=90), 12/24 months before progression (n=72/24) and at the time of progression (n=52) are available. TK1 concentration in plasma samples was measured by competitive ELISA (ABIN809094, Shanghai BlueGene Biotech Co., LTD, China) and TK1 activity of matched plasma samples by competitive, two-step chemiluminescence immunoassay (REF 310960, Diasorin, Stillwater, US). Statistical analysis was conducted via log-rank test and univariate or multivariate Cox regression. Results: Currently, baseline samples were evaluated for TK1 concentration (n=106) and activity (n=90). The mean value for TK1 activity was 12.69 U/L and the median value was 8.37 U/L in the entire cohort. Values ranged from 0.89 to 79.50 U/L and the standard deviation was determined to be 12.64 U/L, which is similar to the mean value. In contrast to the control group, high TK1 activity (Cut-off: mean or determined by ROC analysis and maximal Youden’s Index for PFS < six months) was significantly correlated with decreased progression free survival (PFS) in the CDK4/6i cohort (p-value < 0.05 in log rank test and univariate Cox regression). In addition, using multivariate Cox regression analysis including clinical parameters (e.g. therapy line, prior chemo- or endocrine therapies, type of CDK4/6i accompanying endocrine therapy, number of sites of metastases, visceral metastases, menopausal status), TK1 activity was found to be an independent marker for PFS.High TK1 activity (Cut-off: mean or determined by ROC analysis and maximal Youden’s Index for PFS < six months or already deceased patients) at baseline was significantly correlated with shorter time from baseline to death in the CDK4/6i cohort (p-value < 0.05 in log rank test and univariate Cox regression) but not in the control cohort. For TK1 concentration analysis, the mean value was 21.76 ng/ml and the median value was 18.57 ng/ml in the entire cohort. Values ranged from 7.35 ng/ml to 46.66 ng/ml and the standard deviation was determined to be 11.16 ng/ml, which is half of the mean value. In contrast to TK1 activity measurements, no significant association of TK1 concentration with PFS or overall survival (OS) was detected in the CDK4/6i cohort. Currently, all remaining samples during the course of treatment are evaluated for TK1 activity and concentration and final statistical analysis of the complete data set will be available at the meeting. Conclusion: Our preliminary results indicate that TK1 activity, in contrast to TK1 concentration, determined before starting CDK4/6 inhibtion could be a suitable predictive and prognostic biomarker for estimating response to treatment. Our final analysis will clarify, whether TK1 could also serve as a monitoring marker during treatment. Citation Format: Stefanos Moukas, Merle Dohn, Rainer Kimmig, Mitra Tewes, Hans-Christian Kolberg, Sabine Kasimir-Bauer, Corinna Keup. Do thymidine kinase 1 (TK1) plasma concentration and activity play a role in therapy management of metastatic breast cancer patients treated with CDK4/6 inhibitors? [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P5-02-50.

Abstract OT3-11-01: TK IMPACT: Treatment Monitoring of Hormone Receptor Positive (HR+), HER2 Negative (HER2-) Metastatic Breast Cancer (MBC) Patients Receiving CDK 4/6 Inhibitors (CDK4/6i) with DiviTum® Thymidine Kinase 1 Activity

Abstract Background: CDK 4/6i have altered the therapeutic landscape of HR+, HER2- MBC, improving progression free and overall survival (PFS and OS) compared to endocrine therapy (ET) alone. Despite durable responses to CDK 4/6i in a large majority of patients, treatment response monitoring in this population has historically included numerous serial blood-based and imaging studies at frequent time points. There is a growing global interest in utilizing novel non-invasive biomarker-driven disease monitoring assessments to improve patient outcomes and reduce health care costs. Thymidine kinase 1 (TK1), a key cell-cycle regulated enzyme important for nucleotide metabolism during DNA synthesis, is regulated by the E2F pathway, downstream of CDK 4/6. Studies have shown that DiviTum® TK1 activity (TKa) may serve as both a prognostic and predictive biomarker of CDK 4/6i treatment response (McCartney et al, Clin Canc Res, 2020; Malorni et al, Eur J Cancer, 2022; Bagegni et al, Breast Cancer Res, 2017). Early TKa suppression within 2 weeks (wk) post CDK 4/6i therapy initiation is associated with improved PFS, suggesting a subgroup of patients who may be able to de-escalate imaging frequency. Elevated TKa at baseline and post CDK 4/6i may identify patients with CDK 4/6i-resistant disease and disease progression (PD) requiring early therapy modification. TK IMPACT is a prospective, single-arm trial designed to assess the impact of incorporation of DiviTum® TKa on a physician’s decision regarding subsequent timing of routine disease monitoring modalities in patients with advanced HR+, HER2- MBC receiving ET plus CDK 4/6i (NCT04968964). Methods: Blood sample collections will be analyzed using DiviTum® TKa at baseline (bl), wk 2, 4, 6, 8, and Q 4 wks thereafter beginning at wk 8 during the first 24-wk time period of study enrollment (+/- 3 days); followed by Q 12 wks thereafter, until PD or 36 months, whichever occurs first. Optional repeat TKa within 2-4 wks (+/-3 days) is permitted in case of rising TKa. Research blood (bl, wk 2, 12, 24, 48, and PD) and optional archival tumor tissue collection at diagnosis and PD will be obtained for correlatives. The investigator will record intended imaging modalities and timing prior to receipt of TKa, followed by documentation of any changes in imaging testing interval after receipt of TKa. Key eligibility criteria include postmenopausal women age ≥18 years with HR+, HER2- MBC, to initiate (Cohort 1) or are currently receiving (≤24 months, Cohort 2) any FDA approved first line ET plus CDK 4/6i with a life expectancy > 6 months. The primary endpoint is any physician-reported intended change in imaging testing interval post TKa by study cohort, within the first 48-wk period of study participation. Key secondary endpoints are concordance rate between TKa values and progression status at first on-study imaging and longitudinal TKa dynamics. Key exploratory endpoints include plasma and tumor tissue-based biomarkers of CDK 4/6i response and resistance. A total of 40 patients will be enrolled (n=20/Cohort). The expected change rate is 20% with a 95% Wilson confidence interval of 0.105~0.248 across all patients and if within each cohort, with a 95% Wilson confidence interval of 0.081~0.416 for N=20. N=40 allows the lower limit of the 95% CI > 10% and that of the N=20 in Cohort 1 to be ~10%, indicating some clinically meaningful influence of TKa progression on patient management. The study is open to accrual and has presently enrolled 5 patients. Citation Format: Nusayba A. Bagegni, Isabella Grigsby, Leslie Nehring, Jingqin Luo, Jennifer Powers Carson, David W. Gibson, Meghan Horvath, Katherine K. Clifton, Foluso O. Ademuyiwa, Rama Suresh, Ashley Frith, Andrew A. Davis, Lindsay L. Peterson, Ron Bose, Amy Williams, Mattias Bergqvist, Cynthia Ma. TK IMPACT: Treatment Monitoring of Hormone Receptor Positive (HR+), HER2 Negative (HER2-) Metastatic Breast Cancer (MBC) Patients Receiving CDK 4/6 Inhibitors (CDK4/6i) with DiviTum® Thymidine Kinase 1 Activity [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr OT3-11-01.

Abstract P4-01-19: Real World Statistics on CDK4/6 Inhibitor Use in Metastatic Hormone Receptor Positive and HER2-Negative Breast Cancer with a Focus on Age

Abstract Background: Combining CDK 4/6 inhibitors with hormone directed therapy using aromatase inhibitors (AI) or selective estrogen receptor down-regulators (SERD) is considered first line therapy for treatment of hormone receptor positive (HR+) human epidermal receptor 2 negative (HER2-) metastatic breast cancer (mBC). Here we aim to evaluate first line CDK 4/6 inhibitor practice patterns both nationally and locally (Wisconsin) in HR+ HER2- mBC patients and evaluate age as a potential factor impacting practice patterns. Methods: A retrospective analysis was performed utilizing IQVIA Anonymized Patient Longitudinal Data. The data base captures 60-85% of cancer patients across all 50 states in the United States and relies on diagnostic coding used in service or treatment claim filing. Patients queried were greater than 18 years old and were identified by a code indicating CDK4/6 inhibitor therapy or a combination of codes indicating mBC, HR+ status and HER- status. First line treatment was categorized as CDK4/6 inhibitor combination therapy, AI monotherapy, SERD, selective estrogen receptor modulator (SERM) monotherapy, chemotherapy, or other. Patients were further filtered by year, location, practice type (academic vs community), and age. Results: A total of 313,978 patients with mBC receiving first-line therapy were identified nationally between 2015 and 2021. The proportion of patients on first line CDK4/6 inhibitor combination therapy nationally significantly improved from 20% in 2015 (N=27,063) when palbociclib was first approved, to 53% in 2021 (N=54,023) (Table 1.) In 2021, first line use of CDK 4/6 inhibitor combination therapy was higher at 59% both in WI and our institution Froedtert Hospital and the Medical College of Wisconsin Cancer Center (Table 2.) At our center in 2021, the use of first line CDK4/6 inhibitor combination therapy in patients greater than age 65 was significantly lower at 35% (N=39) compared to patients less than 65 at 75% (N=64.) Further delineating the age groups at our center (Table 3,) use of CDK4/6 inhibitor combination therapy in patients aged 70-79 was 35% (N=20) and fell to 20% in patients greater than 80 in age (N=8.) Conclusion: Despite significant improvement in long-term outcomes with first line CDK4/6 inhibitor combination therapy in HR+ HER2- mBC patients, overall national usage is suboptimal. At our center, this was particularly apparent in patients older than 70. Identifying barriers to optimal use is critical to improve utilization of this important and effective class of drugs. National Percentages of HR+ HER2- mBC Patients Stratified by First Line Treatment Between 2015-2021 HR+ HER2- mBC patients Nationally treated with first line therapy (N=313,978.) National and Local Percentages of HR+ HER2- mBC Patients Stratified by First Line Treatment in 2021 HR+ HER2- mBC patients treated with first line therapy in 2021 Nationally (N=54,026,) in Wisconsin (N=694,) and at Froedtert Hospital and the Medical College of Wisconsin Cancer Center (N=103.) Local Percentages HR+ HER2+ mBC Patients Stratified by First Line Treatment and Age Group HR+ HER2- mBC patients treated with first line therapy in 2021 at Froedtert Hospital and the Medical College of Wisconsin Cancer Center (N=103.) Citation Format: Kathleen Monahan, Sailaja Kamaraju, Yee Chung Cheng, Janet Retseck, Deepika Sriram, John Burfeind, Christopher Chitambar, Lubna N. Chaudhary. Real World Statistics on CDK4/6 Inhibitor Use in Metastatic Hormone Receptor Positive and HER2-Negative Breast Cancer with a Focus on Age [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P4-01-19.

Abstract P6-08-11: Hyperglycemia in Hispanic MBC patients treated with alpelisib: single institution retrospective study

Abstract Background: PIK3CA mutations are found in up to 40% of hormone receptor positive (HR+), human epidermal growth factor receptor 2 negative (HER2-) metastatic breast cancers (MBC). Alpelisib is an orally bioavailable PIK3CA inhibitor approved in combination with fulvestrant based on the SOLAR-1 study. However, uptake has been limited due to toxicity concerns, most commonly hyperglycemia (grade ≥3 was 37% in SOLAR-1 and 28% in the BYLieve study, which evaluated alpelisib after progression on a CDK 4/6 inhibitor). Patients with uncontrolled type 2 diabetes (T2DM) were excluded from both studies [defined as fasting plasma glucose (FPG) level >140 mg per deciliter, or a glycosylated hemoglobin (HgbA1C) level of >6.4%]. Of note, both trials enrolled a majority of non-Hispanic White (NHW) patients. Disparities regarding prevalence of diabetes has been reported among Hispanics (H). The Centers for Disease Control and Prevention reports that H are more likely to have T2DM than NHW (approximately 17% vs 8% respectively). Our study aims to characterize the incidence and management of hyperglycemia in H MBC patients treated with alpelisib. Methods: A retrospective chart review was performed to include patients with HR+ HER2- MBC with a documented PIK3CA mutation treated with alpelisib in combination with fulvestrant at Miami Cancer Institute from 2019-2022. Patients were identified using pharmacy records and the COTA real-world database (RWD, an analytics platform enabling investigation of longitudinal RWD). Cases were excluded where the start date was unclear, or treatment was given for a diagnosis other than breast cancer. Based on available data in the medical record, patients were categorized as H or NH. Descriptive statistics were used to describe variables in both groups of patients. Results: Of 46 patients identified, 34 were included in the final analysis (17 H and 17 NH). The median age was 63 y (range 32-87). The most common PIK3CA mutation identified was H1047R (41.2% of H and 23.5% of NH; p > 0.05). Starting body mass index (BMI) was higher in H compared to NH (29.9 vs 24.8; p < 0.05). Starting FPG was the same for both groups (115 mg/dL), and within the first two weeks on treatment the highest FPG was higher in H vs NH (250 mg/dL vs 157 mg/dL; p > 0.05). H also had the highest peak glucose when compared to NH (333.8 mg/dL vs 217.8 mg/dL; p < 0.05). Furthermore, by the end of treatment H had a higher FBG than NH (247.4 mg/dL vs 118.0 mg/dL; p < 0.05). Overall, any grade hyperglycemia occurred in 70.6% (82.4% H, 58.8% NH; p > 0.05, with high rates of grade 3/4 hyperglycemia in both groups (53% H 41% NH; p > 0.05). A higher percentage of H patients required more than one anti-hyperglycemic medication as compared to NH (41% vs 12%; p > 0.05). Hispanics time on treatment was shorter compared to NH (151 vs 240 days; p > 0. 05). Disease progression was the most frequent reason for treatment discontinuation in both groups 52.9%. However, more H patients discontinued alpelisib due to hyperglycemia (23.5% vs 5.9%; p > 0.31). Conclusions: Despite starting treatment with similar FPG levels, H had a higher peak plasma glucose level compared to NH. Although not statistically significant, likely due to a small sample size, the rates of hyperglycemia within two weeks of treatment was higher in H than NH. Furthermore, H required the use of more antiglycemic medications and had higher discontinuation rates. Therefore, there is a heightened need to increase education and awareness of glucose monitoring in H during treatment with alpelisib. Further prospective studies are warranted to better define the optimal management of hyperglycemia in H patients. Citation Format: Yolcar Chamorro, Reshma Mahtani, Shanada Monestime, Manmeet Ahluwalia, Muni Rubens, Natasha Harpalani, Ana Sandoval-Leon. Hyperglycemia in Hispanic MBC patients treated with alpelisib: single institution retrospective study [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P6-08-11.

Abstract P4-07-20: Effect of prior treatments on post-CDK 4/6 inhibitor overall survival in hormone receptor positive breast cancer

Abstract Purpose: There are multiple treatment options for patients with metastatic breast cancer (MBC); however, there is minimal data on the optimal sequencing. Furthermore, limited information is available to understand the influence of prior treatment duration and class on novel therapies in real-world settings, such as cyclin-dependent kinase 4/6 inhibitors (CDK 4/6i) for patients with hormone receptor-positive, human epidermal growth factor receptor 2- negative (HR+ HER2-) MBC. Our study sought to identify the effect of prior treatments on post-CDK 4/6i survival. Methods: This retrospective study used the nationwide, de-identified electronic health record-derived Flatiron Health database of women with HR+ HER2- MBC who received at least one CDK 4/6i between 2011 and 2020. Hazard ratios (HR) and 95% confidence intervals (CI) were estimated for the association between duration and class of all cancer treatments prior to receipt of CDK 4/6i and overall survival (OS) adjusting for age at diagnosis, race and ethnicity, site of metastasis, and metastatic diagnosis year. Time dependent HRs were used to compare the OS for patients receiving one versus multiple CDK 4/6i. Results: Of 5,363 patients, most were aged 55-64 (29%), White (69%), and had visceral metastasis (70%). The median survival from receipt of first CDK 4/6 inhibitor was 3.3 years. When compared to patients with no prior treatments, patients with up to one year of prior treatments had a 30% increased hazard of death ((HR, 1.30; 95% CI 1.15-1.46; Table 1). Similarly, patients with one to less than three years of prior treatment had a 68% increased hazard of death (HR 1.68; 95% CI 1.49-1.88) and those with three or more years had a 55% increased hazard of death (HR 1.55; 95% CI 1.36-1.76). Furthermore, patients who received prior endocrine therapy alone experienced a 29% increased hazard of death (HR, 1.29; 95% CI 1.16-1.44), while patients receiving prior chemotherapy experienced a 72% increased hazard of death (HR, 1.72; 95% CI 1.54-1.93) when compared with patients who did not receive a prior treatment. Finally, patients who received a different CDK 4/6i after their first had a 17% decreased hazard of death compared to patients who received subsequent endocrine or chemotherapy after their first CDK 4/6i (HR, 0.83; 95% CI 0.71-0.96). Conclusion: Prior treatment duration and class are associated with a decreased overall survival after CDK 4/6 inhibitor administration. However, patients receiving more than one CDK 4/6 inhibitor in their sequence saw survival benefits. This highlights the importance for clinicians to consider prior treatment and duration in treatment decision-making and for trialists to stratify by these factors when reporting results of future studies. Table 1: The association between OS and treatment duration and class before CDK 4/6 Citation Format: Jeffrey Franks, Nicole E. Caston, Ahmed Elkhanany, Travis Gerke, Andres Azuero, Gabrielle B. Rocque. Effect of prior treatments on post-CDK 4/6 inhibitor overall survival in hormone receptor positive breast cancer [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P4-07-20.

Abstract P2-03-14: Tumor-agnostic measurement of ctDNA levels in first line ER+, HER2- metastatic breast cancer patients as a marker for survival

Abstract INTRODUCTION: Circulating tumor cell (CTC) count and levels of circulating tumor DNA (ctDNA) have proven their individual prognostic value in metastatic breast cancer (MBC). Whereas CTCs can be quantified by enumeration, levels of ctDNA are often expressed as the variant allele frequency of the dominant mutation. The modified fast aneuploidy screening test-sequencing system (mFAST-SeqS) estimates ctDNA-load by measuring chromosomal aneuploidy instead of mutations. The mFAST-SeqS method is cheap and provides a comprehensive overview of the tumor genome without prior knowledge on genomic tumor aberrations. Previously, we showed in a small MBC cohort (n=50), heterogeneous with regard to subtype and line of treatment, that the mFAST-SeqS-derived genome-wide aneuploidy score (GWA-score) was an independent prognostic biomarker (1). Our current aim was to provide evidence for the prognostic value of GWA-score in a homogeneous cohort of estrogen receptor positive (ER+), HER2 negative (HER2-) MBC patients, starting first line treatment with an aromatase inhibitor. MATERIALS & METHODS: CTCs were enumerated using the CellSearch-system (Menarini) and screened for ctDNA fraction using mFAST-SeqS in ER+, HER2- MBC patients, starting with first line aromatase inhibitors. CTC-count was divided into high (CTChigh) and low (CTClow) using the validated cut-off of 5 CTCs/7.5 ml blood; similarly GWA-score was divided in high (GWAhigh)and low (GWAlow) based on the previously described cut-off of 5 (2). PFS and OS were estimated using Kaplan-Meier. Cox regression was used for uni- and multivariable analysis. RESULTS: One hundred and thirty-four patients were included in this analysis. Mean age was 68 (range 40-90). Median follow up was 26 months. Sixty-five samples had both scores low and 30 both high, 25 samples were CTChigh/GWAlow and 14 were CTClow/GWAhigh. PFS and OS were not significantly different between CTChigh versus CTClow groups (p=0.07 and p=0.26, median PFS 15 vs 24 months, median OS 45 vs 49 months). However, PFS and OS were significantly different between GWAhigh versus GWAlow groups (p < 0.01 for both, median PFS 11 vs 24 months, median OS 31 vs 51 months). In multivariate analysis, GWA-score was a significant prognostic factor for both PFS and OS while presence of visceral disease was also prognostic for OS (table 1). CONCLUSIONS: In patients treated with aromatase inhibitors in the first line of treatment, GWA-score was an independent prognostic marker for a worse PFS and OS and may have added value beyond CTC-count. 1. Verschoor, N., et al., Abstract P2-01-17: Circulating tumor cell count and levels of circulating tumor DNA are complementary prognostic biomarkers in metastatic breast cancer - A pilot study. Cancer Research, 2022. 82(4_Supplement): p. P2-01-17-P2-01-17. 2. Belic, J., et al., mFast-SeqS as a Monitoring and Pre-screening Tool for Tumor-Specific Aneuploidy in Plasma DNA. Adv Exp Med Biol, 2016. 924: p. 147-155. Table 1: Uni- and multivariate Cox regression for PFS and OS Citation Format: Noortje Verschoor, Jaco Kraan, Vanja de Weerd, Ngoc M Van, Agnes Jager, Stefan Sleijfer, John WM Martens, Saskia M Wilting. Tumor-agnostic measurement of ctDNA levels in first line ER+, HER2- metastatic breast cancer patients as a marker for survival [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P2-03-14.

Abstract P3-07-14: A phase II study of CFI-400945 in patients with advanced/metastatic cancer: Canadian Cancer Trials Group (CCTG) IND.237

Abstract Background: CFI-400945 is a selective oral inhibitor of Polo-like Kinase 4 (PLK4), a controller of centriole duplication and mitotic progression identified by functional screening of genomically unstable breast cancer (BC). IND.237 (NCT01954316) is an open label, multicentre, phase 2 study in HER2 negative metastatic breast cancer (MBC) with 3 cohorts, 1 enriched for PTEN loss of function. Enrollment started in 2018 at 64mg based on a previously established recommended phase 2 dose (RP2D). The initial patients had higher than expected grade 3/4 neutropenia which led to a voluntary hold and dose de-escalation; the new RP2D was declared at 32mg as previously reported Here we report the results of the phase 2 study of CFI-400945 in advanced BC patients. Materials and Methods: 49 patients were enrolled across 3 cohorts: 1: triple negative; 2: ER+/HER2- PTEN low (by IHC); 3: ER+/HER2-, PTEN intact. The primary outcome is objective response rate (ORR); secondary outcomes included disease control rate (DCR) >16w, and safety. A Simon 2-stage design was used (9 – 25 pts planned for each cohort). CFI-400945 would be considered active if ≥3 responses were observed in any given cohort. Eligibility included ECOG 0-1, adequate organ function and receipt of at ≥1 prior line of cytotoxic chemotherapy in any setting including anthracycline taxane (unless contraindicated). Treatment was 32mg 7d on 7d off in cycle 1 (cycle length=28d), then continuously starting cycle 2. Safety assessments were performed each cycle and response (RECIST 1.1) every 2 cycles. Results: 60 patients have been screened, 49 enrolled: 10 were in initial dose ranging and were excluded from phase 2 response assessment. 10 patients were enrolled in cohort 1, 4 in cohort 2, and 25 in cohort 3. Table 1 presents patient characteristics and response results. 1 patient in cohort 3 has not had disease re-assessed at time of abstract submission. The most common adverse events have been cytopenias, nausea, fatigue, headache, constipation and vomiting. Less than 5% of patients experienced a non-hematologic AE > grade 3; 33% experienced ≥ grade 3 neutropenia. Conclusions: CFI-400945 32mg is well tolerated in this MBC population with moderate incidence of uncomplicated neutropenia. The TNBC cohort so this arm has been closed to further accrual for lack of responses. The PTEN loss group has been slow to accrue and remains open. Responses in the ER+/HER2- arm are encouraging – results from patients remaining on study are awaited and correlative studies to identify features associated with responses are underway. Acknowledgements: Sponsored by the Canadian Cancer Trials Group. Supported by Stand Up To Cancer Canada (scientific partner AACR) Canadian Cancer Society (CCS) Breast Cancer Dream Team Research Funding, Ontario Institute for Cancer Research (funding provided by the Government of Ontario) and grants from CCS to CCTG. Table 1. Table 1. Patient characteristics and response rates in each cohort treated with CFI-400945. Citation Format: David W. Cescon, John Hilton, Philippe Bedard, Phillip Blanchette, Rossanna C. Pezo, Ayesha Bashir, Vikaash Kumar, Terry L. Ng, Arif Awan, Anthony Lott, Jacques Antoun Raphael, Linda Hagerman, Mark Bray, Lindsay Muyot, Jesus Fuentes Antras, Lesley Seymour, Dongsheng Tu, Pierre-Olivier Gaudreau, Moira Rushton. A phase II study of CFI-400945 in patients with advanced/metastatic cancer: Canadian Cancer Trials Group (CCTG) IND.237 [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P3-07-14.

Abstract P2-01-08: The Efficacy of Anlotinib Combined with TEC in Neo-adjuvant Treatment for Triple-Negative Breast Cancer and The Value of Multi-point Core Needle Biopsy in Prediction of Pathologic Complete Remission: A Retrospective analysis

Abstract background While neo-adjuvant anthracycline and taxane-based chemotherapy remains the standard of care for locally advanced TNBC, the optimal chemotherapy regimen is debatable. Anlotinib, a novel multi-target tyrosine kinase inhibitor that effectively inhibits VEGFR, FGFR, c-KIT, c-MET, and RET, monotherapy has been proven effective in HER-2 negative metastatic breast cancer. This study aims to evaluate the efficacy and safety of anlotinib combined with TEC in neo-adjuvant treatment for locally advanced TNBC, and to evaluate the value of predicting pathological response by multi-point core needle biopsy during neo-adjuvant therapy. method This study retrospectively analyzed 18 patients (Pts) with locally advanced triple-negative breast cancer who received anlotinib combined with TEC neo-adjuvant therapy and surgical treatment from August 2020 to January 2022 in the Breast Diagnosis and Treatment Center of Anhui Cancer Hospital. Pts with clinical stage IIb/III TNBC were to be treated with 6 cycles of anlotinib (12mg, d1-14, q3w) plus 6 cycles of docetaxel (75 mg/m2, d1, q3w), Epirubicin (90 mg/m2, d1, q3w) and cyclophosphamide (600 mg/m2, d1, q3w) followed by surgery. Before the fifth cycle of treatment, ultrasound-guided multi-point Core needle biopsy was performed to evaluate the efficacy of neo-adjuvant therapy and predict the pathological complete response, as well as to guide the selection of surgical methods. The primary endpoint was pathological complete response (pCR, ypT0/is). Result Eighteen pts, the median age was 48 years (range, 23-60), were included in the statistical analysis. All patients completed 6 cycles of anlotinib combined with TEC neo-adjuvant therapy followed by radical mastectomy for breast cancer. Regarding pathological response, there were 4 (22.2%), 2 (11.1%), and 12 (66.7%) patients realizing Miller-Payne grade G3, G4, and G5, respectively. Besides, 12 (66.7%) patients achieved pCR. Additionally, the accuracy of multi-point core needle biopsy in predicting pCR was 94.4% in the interval between neo-adjuvant therapy. The grade 3 or 4 AEs were neutropenia and thrombocytopenia in 3 cases each, anemia, arrhythmia, and ALT increased in cases 1 case each. One patient dropped out of the group due to tumor rupture and bleeding. conclusion Anlotinib combined with TEC as neo-adjuvant therapy showed manageable toxicity and promising antitumor activity for locally advanced TNBC. It is safe, reliable, feasible and accurate to evaluate the efficacy of neo-adjuvant therapy and to predict pathological complete response by multi-point core needle biopsy. It means that the clinical evaluation of neo-adjuvant therapy can transition from imaging evaluation to pathological evaluation, which is helpful for the choice of surgical methods. Citation Format: Kuojun Ren, Shikai Hong, Zhengzhi Zhu, Shengying Wang, Jianjun Liu, Hong Gao, Shuhan Wang. The Efficacy of Anlotinib Combined with TEC in Neo-adjuvant Treatment for Triple-Negative Breast Cancer and The Value of Multi-point Core Needle Biopsy in Prediction of Pathologic Complete Remission: A Retrospective analysis [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P2-01-08.

Abstract P4-01-13: A retrospective study of anlotinib in patients with HER-2 negative metastatic breast cancer after prior two or more lines treatment

Abstract Background: Anlotinib is a novel small molecule antiangiogenic drug that can inhibit multiple tyrosine kinase receptor activities. It has demonstrated antitumor activity in various cancers. This retrospective study explored the efficacy and safety of anlotinib combined chemotherapy in HER-2 negative metastatic breast cancer patients who have disease progressed after prior two or more lines of therapy. Methods: This retrospective study enrolled twenty-two HER-2 negative metastatic breast cancer patients including TNBC and HR+ subtypes. These patients pretreated with at least two lines of chemotherapy and/or endocrine drugs before receiving anlotinib. These patients received anlotinib combination with investigator-selected chemotherapy agents, including docetaxel, vinorelbine, gemcitabine, etoposide, alibrine and so on. Anlotinib was administered 12mg d1-d14 for a 21-day cycle. The primary end point of this study was progression free survival (PFS). Secondary end points included objective response rate (ORR), disease control rate (DCR), overall survival (OS), and toxicity. The treatment continued until disease progression or intolerability or the patient withdraw informed consent. Results: The enrolled breast cancer patients received anlotinib with a median age of 52.5 (rang 30 to 73). The patients with multiple metastases were 59.1% (13/22). All patients were evaluated and the ORR was 50% (95% Cl 0.282-0.718), DCR 95.5% (95% Cl 0.772-0.999) and the mPFS was 8 months (95% Cl 5.15-10.85). We also analyzed the efficacy of anlotinib combination with chemotherapy in different subtypes. For HR+HER2- metastatic breast cancer patients, the ORR was 77.8% (95% Cl 0.4-0.972), DCR 100% (95% Cl 0.664-1.0) and the mPFS was 8.5 months (95% Cl 7.217-9.783). And for TNBC patients, the ORR was 30.8% (95% Cl 0.091-0.614), DCR 92.3% (95% Cl 0.640-0.998) and the mPFS was 6 months (95%Cl 4.405-7.595). The most common adverse events were grade 1/2 including fatigue, hand-foot syndrome and thrombocytopenia et.al., and no serious adverse events occurred. Conclusion: Anlotinib is safe and effective in patients with HER-2 negative metastatic breast cancer after prior two or more lines treatments, and it is well tolerated. Citation Format: Jing Sun, Yijun Tang, Xiaohui Liu, Jiangli Li, Jin Xia, Liang xu, Junlan Guo, Jing Wang, Shengnan Guo, Zhaojie Sheng, Yanfang Zhang, Yuan Yuan. A retrospective study of anlotinib in patients with HER-2 negative metastatic breast cancer after prior two or more lines treatment [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P4-01-13.

Abstract P6-05-35: Cost-effectiveness of CDK4/6 inhibitors in the first-line treatment of HR+/HER2- metastatic breast cancer in postmenopausal women in Panama

Abstract Background: 4/6 kinase-dependent cyclin inhibitors have been approved for use in combination with first-line aromatase inhibitors in patients with hormone-sensitive, Her 2neu negative metastatic breast cancer. These agents have significantly improved progression-free survival compared to monotherapy aromatase inhibitors. The purpose of this study was to evaluate the cost-evaluation of each of these new agents (palbociclib, ribociclib, and abemaciclib) in the first line in Panama with the perspective of the National Oncological Institute. Methods: A partition survival analysis was carried out that includes three states (free of progression, progression, and death) with cycles of one month and a time horizon of 7.5 years. The efficacy data were taken from pivotal clinical trials, and the costs were estimated locally. A deterministic and probabilistic sensitivity analysis of the Monte Carlo was performed. Results; According to the base case, the update of each of these strategies involved an increase of USD 355,184 per additional QALY for ribociclib with Letrozole compared to Letrozole; USD 944,148/additional QALY for Palbociclib plus Letrozole; and USD 223,956 for Abemaciclib plus Letrozole, when compared with Letrozole, all above the availability threshold to pay 50,000/QALY. Conclusion: Despite the improvement in progression-free survival, none of the strategies have proved cost-effectiveness in our setting. Price negotiations, cost reduction, and risk-sharing agreements between pharmaceutical companies and payers might improve access to new drugs in countries with limited resources. Citation Format: Omar O. Castillo-Fernandez, Maria Lim, Lilian Montano. Cost-effectiveness of CDK4/6 inhibitors in the first-line treatment of HR+/HER2- metastatic breast cancer in postmenopausal women in Panama. [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P6-05-35.

Abstract P2-03-17: Fluoroestradiol (FES) and Fluorodeoxyglucose (FDG) PET imaging in patients with ER+, HER2+ or HER2- metastatic breast cancer

Abstract Background: 18F-Fluorodeoxyglucose (FDG) has long been used for measuring tumor glycolytic activity in clinical PET imaging. The FDA recently approved 18F-Fluoroestradiol (FES) (Cerianna) as a PET imaging tracer for characterizing disease in patients with estrogen-receptor positive (ER+) breast cancer. As FES PET enters clinical practice it is important to establish its utility in the full population of hormone-receptor positive patients, including for patients with human epidermal growth factor 2 (HER2)-overexpressing tumors. Patients with HER2-positive metastatic breast cancer have historically been treated with combination cytotoxic and HER2-directed therapy, with the understanding that HER2 is the primary driver in this disease state. This retrospective study examined uptake in matched lesions for both FES and FDG PET and compared activity in patients with HER2 positive versus HER2 negative metastatic breast cancer. Methods: Patients were selected from the UW research database who had a history of biopsy-proven primary ER+ breast cancer as well as FES and FDG PET scans within 30 days. We examined FDG and FES scans and recorded SUVmax in up to 16 matched lesions between the two scans. Patients were also divided by HER2 status (+/-). In addition, a subset of patients who underwent at least 2 paired FDG and FES scans were reviewed. Results: 270 matched FDG and FES scans were analyzed in 216 patients with history of ER+, and HER2+ or HER2- breast cancer who were not part of an ongoing clinical trial. 158 (73%) had ductal disease, 38 (18%) had lobular disease. 183 (85%) had HER2- breast cancer. Of the 33 patients who had HER2+ breast cancer, 28 (85%) had ductal carcinoma. 40 patients underwent serial scans, allowing tracking over multiple timepoints. A total of 1323 metastatic sites were recorded (average = 5/scan (range 1,16)), with the majority (71%) representing bony lesions. No difference in quantitative FES or FDG avidity was observed between soft tissue and osseous sites. FES and FDG SUVmax were similar among patients with either HER2- or HER2+ breast cancer (Table 1). Among 40 patients with multiple paired FDG and FES scans, 26 (65%) had 2 scans while the remaining 14 had 3, with FES avidity remaining stable over time. There was no correlation between FES or FDG scans and HER2 status. Conclusion: In a cohort of ER+, HER2+ and HER2- patients undergoing concurrent FDG and FES PET scans, FDG and FES activity was similar regardless of HER2 status. FES uptake in both HER2- and HER2+ patients and stability over time in serial scans suggest that HER2 does not affect ER density. This suggests that in many patients with so-called “triple positive” disease, endocrine therapy may offer a powerful primary rather than ancillary tool in select patients. FES combined with FDG PET may offer utility in predicting and assessing response to therapy in this patient population. Table 1. FES and FDG uptake in patients with HER2- or HER2+ disease Citation Format: Natasha Hunter, Lanell M. Peterson, David A. Mankoff, Mark Muzi, Delphine Chen, William R. Gwin, Shaveta Vinayak, Nancy E Davidson, Jennifer M. Specht, Hannah Linden. Fluoroestradiol (FES) and Fluorodeoxyglucose (FDG) PET imaging in patients with ER+, HER2+ or HER2- metastatic breast cancer [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P2-03-17.

Abstract P5-10-01: Phase 2 study of anlotinib combined with taxanes and lobaplatin in the neoadjuvant treatment of triple-negative breast cancer: efficacy, safety and biomarker analysis from the SWH-B006 (neoALTALL) trial

Abstract Background: Anlotinib, a novel multi-target tyrosine kinase inhibitor that effectively inhibits VEGFR, PDGFR, FGFR, c-KIT, c-MET, and RET, monotherapy has been proven effective in HER-2 negative metastatic breast cancer, but its efficacy in early-stage triple-negative breast cancer (TNBC) is unknown. This phase 2 study aims to evaluate the efficacy and safety of adding anlotinib to neoadjuvant chemotherapy in patients (pts) with primary TNBC. Methods: Pts with clinical stage II/III TNBC were to be treated with 5 cycles of anlotinib (12mg, d1-14, q3w) plus 6 cycles of taxanes (docetaxel 75 mg/m2 or nab-paclitaxel 125 mg/m2, d1 and d8, q3w) and lobaplatin (30 mg/m2, d1, q3w), followed by surgery. The primary endpoint was pathological complete response (pCR) in the breast and axilla (tpCR; ypT0/is ypN0) and the secondary endpoints include pCR in the breast (bpCR; ypT0/is), event-free survival (EFS), invasive disease-free survival (iDFS), overall survival (OS), and safety. Exploratory study included biomarker analysis and efficacy comparation based on FUSCC classification (IHC-based). Results: From Jan 2021 to Feb 2022, a total of 24 pts were enrolled. The median age was 50 years (range, 26-64), 54% were postmenopausal, 75% were nodal involved, 29% had stage III, and 79% were Ki-67 high (≥30%). At the data cut off time of 30th Jun 2022, all 24 pts received at least one dose of study treatment and underwent surgery. Overall, 21 pts received five courses of anlotinib. Two pts discontinued anlotinb for safety reason, and one pt discontinued anlotinb due to missed dose in cycle 4. After surgery, 14 out of 24 pts achieved a tpCR (58.3%; 95% CI, 36.6%–77.9%), and the bpCR rate was also 58.3% (14/24). Of the 18 pts with the node-positive disease at diagnosis, 15/18 (83.3%) became ypN0. Based on the FUSCC IHC-based subtypes, the tpCR rates were 66.7% (6/9) for BLIS subtype, 80% (4/5) for IM subtype and 0% (0/4) for LAR subtype, respectively. Next-generation sequencing revealed that the most commonly mutated genes in these pts were TP53 (19/21, 90.5%), MYC (7/21, 33.3%), BRCA1 (5/21, 23.8%), PIK3CA (4/21, 19.0%), BCL2L11 (4/21, 19.0%), and RB1 (3/21, 14.3%). Subgroup analysis showed that the tpCR were 71.4% (5/7) and 42.9% (6/14) in MYC-amplified and wild-type pts, respectively, and 80% (4/5) and 43.8% (7/16) in BRCA1-mutated and wild-type pts, respectively. All of 24 pts in the safety population showed at least one treatment emergent adverse events (TEAEs). Grade 3 or 4 TEAEs occurred in 14 pts (58.3%), and the most common events were leucopenia (29.2%; n=7), neutropenia (29.2%; n=7), thrombocytopenia (20.8%; n=5), anemia (16.7%; n=4), hypertension (12.5%; n=3), and oral mucositis (8.3%; n=2), respectively. No treatment-related deaths occurred. Conclusions: The addition of anlotinib to neoadjuvant chemotherapy showed manageable toxicity and promising antitumor activity for pts with early-stage TNBC. The study is still ongoing, and the enrollment has been completed. Clinical trial information: ChiCTR2100043027. Funding: Chia Tai Tianqing Pharmaceutical Group Co., Ltd. L. Corresponding author: Dr. Xiaowei Qi, qxw9908@foxmail.com. Department of Breast and Thyroid Surgery, Southwest Hospital, Army Medical University, Chongqing. Citation Format: Yan Liang, Jing Liu, Tao Luo, Jia Ge, Hao Tian, Guozhi Zhang, Linjun Fan, Lin Ren, Li Chen, Peng Tang, Kai Zhu, Xiuwu Bian, Jun Jiang, Yi Zhang, Xiaowei Qi, Peng Tang, Kai Zhu, Xiuwu Bian, Jun Jiang, Yi Zhang, Xiaowei Qi. Phase 2 study of anlotinib combined with taxanes and lobaplatin in the neoadjuvant treatment of triple-negative breast cancer: efficacy, safety and biomarker analysis from the SWH-B006 (neoALTALL) trial [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P5-10-01.

Abstract P4-07-24: Circulating tumor cells enumeration and Health Related Quality of Life of patients treated with first-line chemotherapy for HER2 negative metastatic breast cancer

Abstract Background: In patients with metastatic breast cancer (mBC), Circulating Tumor Cells (CTC) counts have a strong prognostic impact on progression free survival (PFS) and overall survival (OS). Changes 4 weeks after the start of a new line of therapy, inform on treatment efficacy. Despite improvements in systemic treatment, metastatic BC remains mainly uncurable with alteration of health-related quality of life (HRQOL) during the course of the disease. The aim of this work was to assess impact of clinical factors and biological factors as CTC on HRQOL. Methods: The French cohort COMET is a prospective study including first line HER2 negative patients receiving weekly paclitaxel and bevacizumab according to EMA approved combination. The aim of this cohort was to evaluate clinical, biological and radiological parameters associated with patients’ outcome (CTC, CEC, serum markers, ctDNA, pharmacogenomic polymorphisms, metabolomic parameters, visceral fat assessed by initial CTscan, serum estradiol level, and quality of life). HRQOL was assessed at baseline, at every cycle until progression and then every 3 months up to death using the EORTC QLQ-C30 questionnaire and its breast cancer specific module, the EORTC QLQ-BR23. Five dimensions of HRQOL were analyzed for the primary analyses: Global health status (GHS), physical functioning (PF), Emotional functioning (EF), fatigue (FA) and pain (PA). Time until definitive deterioration (TUDD) in HRQOL was defined as the interval between inclusion and the first decrease in HRQOL score ≥ 5 compared to baseline HRQOL score with no further improvement or in case of death. CTC counts were determined using the standard CellSearch system [Menarini Silicon Biosystems]. Results: Out of 510 patients included in COMET study, 432 patients with available HRQOL data were analyzed in this study. At baseline, patients reported a mean score for GHS of 57.6 (SD=22.7), for PF of 75.8 (23.2), for EF of 62.2 (25.8), for FA of 42.2 (29.60) and for PA of 38.1 (31.5). The Median TUDDs for the 5 targeted dimensions was 10.1 months [7.5-16.9] for GHS, 6.1 months [4.1-8.9] for PF, 21.6 [18.7-31.2] for EF, 10.8 [6.2-16.6] for FA and 13.6[10.1-22.5] months for PA. CTC counts were available in 261 patients at base line and in 229 patients after 4 weeks of treatment, before second cycle of chemotherapy. CTC high count was independent of main clinical and biological characteristics except lobular subtype. We confirmed the poor outcome of patients with high CTC count at base line and after one cycle of treatment with the threshold of > 4CTC/7.5 ml of blood. Out of the 5 dimensions of HRQOL, TUDD of EF was significantly correlated with a high CTC level at base line (p=0.0262) and even more with still an elevated count of CTC after one cycle of chemotherapy(p=0.0137). There was no association of CTC with the other dimensions of HRQOL. Conclusion: This is the first study ever reporting an analysis of QoL and CTC. We observed an association of high CTC count with one component of HRQOL scale. This suggests that CTC could be complementary to clinical factors that could influence HRQOL in HER2 negative metastatic BC treated with first line chemotherapy. Citation Format: Jean-Yves Pierga, Oumar Billa, Sandrine Dabakuyo, Jérôme Lemonnier, Frédérique Berger, Olivier Trédan, William Jacot, Anthony Gonçalves, Marc Debled, Christelle Levy, Christelle Jouannaud, Marie-Ange Mouret-Reynier, Jean-Marc Ferrero, Florence Dalenc, Fatima-Zohra Toumi, Franck Bonnetain, Francois-Clement Bidard, Shufang Renault. Circulating tumor cells enumeration and Health Related Quality of Life of patients treated with first-line chemotherapy for HER2 negative metastatic breast cancer [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P4-07-24.

Abstract P3-05-45: Circulating tumor cells, immunohistochemical subtypes, and genes mutation as prognostic markers in HER2 negative metastatic breast cancer patients candidates to chemotherapy

Abstract Background: In the era of targeted therapies, chemotherapy (CT) is still a valuable treatment option for patients (pts) with HER2 negative metastatic breast cancer (MBC). The identification of predictive and prognostic markers might improve treatment response and survival. Here we investigated the role of tumor subtypes, circulating tumor cells (CTCs), and mutations in genes or pathways of interest, in predicting response to CT and prognosis of HER2 negative MBC pts within AARES trial. Methods: AARES is an open label multicentric randomised phase 2 trial comparing a DNA-damaging (arm A: cisplatin 25 mg/m2/day, day 1-3 + cyclophosphamide 600 mg/m2 day 1) versus (vs) a non-DNA-damaging (arm B: capecitabine 1000 mg/m2 bid/day, day 1-14 + vinorelbine 60 mg/m2/day, day 1,8) CT regimen in pts with HER2 negative MBC. Archival tumor tissue samples and blood samples were collected at baseline. The Cell SearchTM system was used for CTCs isolation and enumeration and a cut-off of 5 CTC/7,5 ml was used. Tumor subtypes were based on locally assessed hormone receptors and HER2 status. The luminal-like subtype (Lum) was defined by ER or PR positivity, while the triple negative subtype (TN) by ER, PR, and HER2 negativity. Tissue samples were used for DNA extraction and next generation sequencing analysis using a target enrichment panel of 170 genes (TruSight 170, Illumina). Primary endpoint was objective response rate (ORR) assessed for the two treatment arms. Progression free survival (PFS) and overall survival (OS) were evaluated as secondary endpoints, and estimated with the Kaplan-Meier method. ORR, PFS and OS were correlated with CTC counts, tumor subtypes, and mutational status of genes/pathway of interest (PIK3CA, TP53, BRCA1, BRCA2, PI3K/AKT pathway (PI3K/AKT)). Results: AARES enrolled 102 pts from 2011 to 2016 across 9 Italian centers. Of these, 77 pts were evaluable for ORR. Median follow up was 32 months. Overall, median age was 57. The majority of pts had Lum tumors (73%), while 27% had TN. 86% of pts had visceral metastases, and 52% had 3 or more metastatic sites. 48% of pts received the study treatment as 1st line, 32% as 2nd line, and 19% as 3rd line. Out of the 77 pts with ORR data, 41 (53%) were CTC- and 36 (47%) CTC+. A larger proportion of pts with Lum tumors were CTC+ (54% n=30), while TN tumors were mainly CTC- (71% n=15). 49 pts had adequate tumor tissue for sequencing analysis. TP53 mutations (mut) were found in 33% of pts, BRCA1/2 mut in 14%, PIK3CA mut in 35%, and PI3K/AKT mut in 47%. ORR was 24% and 37% in arm A vs arm B, respectively (p= 0.2), and no difference in ORR was observed by tumor subtypes (Lum vs TN), and CTCs count (+ vs -). PFS and OS were assessable on the whole population (n=102) and did not significantly differ by treatment arms. Median OS (mOS) was higher in Lum pts compared to TN (24 months (mo) vs 15.4 mo, p=0.048) while median PFS (mPFS) did not differ according to tumor subtypes (p=0.28). Overall, CTCs count was not significantly associated with mPFS or OS however in pts with TN tumors and CTC-, mPFS and mOS were significantly longer (mPFS: 4.44 mo vs 2.56 mo in CTC- and CTC+ subgroups, respectively, p=0.00087 and mOS: 22.07 mo vs 3.57 mo in CTC- and CTC+ subgroups, respectively, p< 0.0001). On the other hand, no differences were observed in Lum pts categorized according to CTC status (p=0.83 for mPFS, p=0.54 for mOS). Finally, pts with PI3K/AKT mut had a significantly worse PFS compared to wild type in the overall population (p=0.0091) as well as in Lum (p=0.034) and TN pts (p=0.0052). Conclusions: CTCs and tumor subtypes were not predictive of response to CT regimens in HER2 negative MBC pts. A number of CTC >5 in TN MBC, and mutations in the PI3K/AKT pathway, identified a subgroup of pts with worse prognosis, potentially candidates for alternative treatments. Further studies are needed to confirm these results in a larger population. Citation Format: Emanuela Risi, Marta Pestrin, Chiara Biagioni, Dario Romagnoli, Ilenia Migliaccio, Francesca Galardi, Francesca De Luca, Matteo Benelli, Erica Moretti, Giuseppina Sanna, Luca Livraghi, Silvia Cappadona, Roberta Di Marsico, Domenico Amoroso, Angelo Martignetti, Angela S. Ribecco, Elena Rota Caremoli, Luigi Coltelli, Fabio Puglisi, Luca Malorni, Laura Biganzoli. Circulating tumor cells, immunohistochemical subtypes, and genes mutation as prognostic markers in HER2 negative metastatic breast cancer patients candidates to chemotherapy [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P3-05-45.