Metastatic Breast Cancer Patients Research Articles

Abstract PO4-10-11: Needs of oncology nurse navigators serving young or metastatic breast cancer patients

Abstract Oncology nurse navigators (ONN) facilitate breast cancer patients' care via information, resources, and referral services. Two important groups of breast cancer patients served by ONN are young women with breast cancer (yBC), defined as women diagnosed at age 45 or younger, and metastatic breast cancer (mBC) patients. These two groups of patients have distinct needs for clinical care and services. To better understand the needs and experiences of ONN serving these patients, we surveyed 52 active ONN in the United States via an online needs assessment survey about their familiarity with topics relevant for breast cancer patients, referral patterns, and perception of educational needs. As expected, most ONNs saw more yBC than mBC patients. Familiarity of ONN with topics relevant for yBC and mBC differed based on their work experience. For some topics, earlier-career ONN (<5 years of work experience) reported distinct experiences from later-career ONN (more than 5 years of work experience). Earlier-career ONN were less familiar than later-career ONN with clinical trial participation (45% vs 79%; p=0.0315) and genetic counseling and testing (73% vs 96%; p=0.0431). Most ONN referred yBC and mBC patients for financial, mental health, or genetic testing services. For many other services, referral patterns of yBC and mBC patients differed. Earlier-career ONN referred patients less often than later-career ONN to clinical trials (35% vs 89%; p=.0014 for yBC, and 36% vs 89%, p=.0028 for mBC). Earlier-career ONN tended to refer mBC patients less often than yBC for genetic counseling and testing, healthy lifestyles, menopause management, and sexual health or intimacy services. In contrast, later-career ONN referred yBC and mBC patients at similar rates. ONN reported substantial barriers to many services (but not to fatigue, menopause management, and pain management). The services for which ONN most frequently reported barriers were fertility preservation (predominantly financial and lack of programs/providers) and clinical trial services (patient understanding of value and medical jargon/health literacy barriers). ONN referred patients infrequently to some services despite reporting few barriers in contrast to prior reports of breast cancer patients' needs. Most ONN were interested in continuing education for sexual health and intimacy but not clinical trials, treatment side effects, or pain management. Most ONN cited a need for patient materials about sexual health and intimacy and mental health issues. While most ONN were confident in their ability to address questions about breast cancer in the media, they indicated additional resources would be useful. Understanding barriers to information and referrals is necessary to develop approaches to reduce educational gaps and lower referral barriers. Adapting efforts according to ONN career stage may be an important component for continuing education. For clinical trial participation, patient-friendly materials may help reduce barriers to referral and participation. Citation Format: Kelly Owens, Marleah Dean, Elizabeth Bourquardez Clark, Piri Welcsh, Diane Rose, Erica Kuhn, Jessica Conaty, Robin Pugh-Yi, Susan Friedman. Needs of oncology nurse navigators serving young or metastatic breast cancer patients [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO4-10-11.

Abstract PO5-04-01: Inetetamab combined with sirolimus and chemotherapy in HER2 positive metastatic breast cancer patients with abnormal activation of Pi3k/Akt/mTOR pathway after trastuzumab treatment

Abstract Objective: To explore the efficacy and safety of Inetetamab Combined with Sirolimus and Chemotherapy in the treatment of human epidermal factor receptor 2 (HER2) positive metastatic breast cancer patients with abnormal activation of Pi3k/Akt/mTOR (PAM) pathway after Trastuzumab treatment. Methods: This prospective multicenter clinical study enrolled HER2 positive metastatic breast cancer patients at the National Cancer Center in China from July 2021 to September 2022 with PAM pathway mutation confirmed by histology or peripheral blood genetic testing. The inclusion criteria included: 1) Recurrent and metastatic breast cancer patients with HER2 positive confirmed histologically; 2) ECOG PS score ≤ 2; 3) Patients who have progressed after previous treatment with Trastuzumab; 4) Patients with PAM pathway mutation confirmed by Genetic testing; 5) Patients' cardiac, pulmonary, liver and bone marrow functions are basically normal; 6) Patients voluntarily sign informed consent forms. The exclusion criteria included: 1) Patients previously treated with mTOR inhibitors or pyrotinib; 2) Patients who have used chronic Corticosteroid for more than 3 months or used Immunosuppressive drug within 4 weeks; 3) Patients with symptomatic central nervous system metastasis; 4) Patients with left ventricular Ejection fraction< 50% or clinical manifestations of obvious arrhythmia, myocardial ischemia, severe atrioventricular block, cardiac insufficiency, and severe valvular disease; 5)Diagnosed with other malignant tumors within five years. Patients were randomly divided into trial group and control group. The patients in the trial group received inetetamab combined with sirolimus and chemotherapy, and control group received pyrotinib and chemotherapy. RECISTv1.1 standard was used to evaluate the efficacy of patients. Descriptive statistics are used to summarize clinical pathological features. Kaplan Meier method was used to draw survival curves. Log-rank test was used to compare progression free survival (PFS) differences between groups. P< 0.05 was considered statistically significant. Results:A total of 59 HER2 positive metastatic breast cancer patients with abnormal activation of PAM pathway were included, of which 37 patients received the treatment of inetetamab group and 22 patients received the treatment of pyrotinib group. The median follow-up time was 5.33 months. In the intent-to-treat set, the median PFS of patients in the inetetamab group was 4.64 months, which was shorter than 5.69 months in the pyrotinib group. There was no statistically significant difference between the two groups (P=0.51; HR=0.41; 95% CI, 0.12-1.45). The objective response rate (ORR) of the inetetamab group and the pyrotinib group were 28.1% and 29.4%, respectively. In terms of safety, the incidence of adverse events (AE) in the experimental group was (33/37) 89.1%, while (16/21) 76.2% in the control group. The incidence of AE above level 3 in the inetetamab group and pyrotinib group were (13/37) 35.1% and (3/21) 14.3%, respectively. Conclusion:For the metastatic HER2 positive breast cancer patients with abnormal activation of PAM pathway treated with trastuzumab previously, the combination of inetetamab with sirolimus and chemotherapy regimen are equivalent to the combination of pyrotinib and chemotherapy regimen. It demonstrated that combination of inetetamab with sirolimus and chemotherapy could be one of the treatment options for the metastatic HER2 positive breast cancer patients. Citation Format: Qiao Li, Dan Lv, Xiaoying Sun, Mengyuan Wang, Li Cai, Feng Liu, Chenghui Li, Jiuda Zhao, Jing Sun, Yehui Shi, Fei Ma. Inetetamab combined with sirolimus and chemotherapy in HER2 positive metastatic breast cancer patients with abnormal activation of Pi3k/Akt/mTOR pathway after trastuzumab treatment [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO5-04-01.

Abstract PO5-04-04: Development of a method to detect very low levels of HER2 expression in Circulating Tumor Cells (CTCs) by liquid biopsy in patients with metastatic breast cancer

Abstract Introduction Blood-based liquid biopsies are a non-invasive diagnostic approach for detecting circulating tumor cells (CTCs) or circulating tumor DNA (ctDNA) that may provide clinically actionable information for treatment decisions for metastatic breast cancer (MBC) patients when a conventional tissue biopsy is not feasible. Recently, the novel anti-HER2 antibody-drug conjugate, Trastuzumab Deruxtecan (T-DXd), has shown effectiveness against MBC with low HER2 expression detected by tissue biopsy characterized as HER2-low (immunohistochemically 1+ or 2+ and ERBB2 amplification-negative via in situ hybridization) and is being explored in an ultra-low population. Here we report on the application of a liquid biopsy platform designed to sensitively detect low levels of HER2 protein expression in CTCs from MBC patients. Methods Blood samples from 704 metastatic breast cancer patients as well as control cells lines were collected for cell-based and cell-free DNA analysis. After plasma isolation, nucleated cells deposited on glass slides went through immunofluorescent staining and imaging. CTCs were identified using Epic Sciences’ digital imaging and machine learning algorithms, and a subset of CTCs were isolated and sequenced for genomic quantification of large scale-state transitions (LSTs) as well as copy number variants (CNVs). The HER2 status was based upon on ASCO-CAP guidelines and the previous tissue biopsy results from the ordering healthcare provider, as documented on the DefineMBC™ test requisition form. Results Within a DefineMBC early-access program (EAP), 93% of patients with MBC had detectable CTCs. Among ERBB2-non-amp patients tested with the DefineMBC assay, 25% of patients with MBC had findings that were reported as consistent with HER2-low in the CAP-CLIA setting. To explore the lower boundaries of HER2 protein expression, we created and validated an MCF-7 HER2-negative ERBB2 knock-out cell line and utilized its 95% confidence level threshold (271 MFI) as a negative fluorescence cutoff for very low HER2 expression. Based upon publicly available CCLE datasets, MDA-MB-453, MCF7, and MCF7 ERBB2 KO breast cancer cell lines were selected for their high and low HER2 RNA expression levels and were corroborated via observed HER2 immunofluorescence median levels of 15740, 381, and 188 MFI respectively. In an exploratory analysis, among ERBB2-non-amp patients, we retrospectively applied the 271 MFI HER2 cutoff to the EAP cohort and identified 38% of patients with very low HER2 expression. We examined the impact of the HER2 ultra-low cutoff in patients not eligible for T-DXd treatment. Among patients reported as IHC=0 or with unknown IHC status from the most recent tissue biopsy, 44% and 42%, respectively, may qualify for treatment with T-DXd. Conclusion Using our higher sensitivity assay that combines CTC immunofluorescence and single-cell genomic analysis, we examined the lower boundary of HER2 protein expression. Feasibility data support further characterization of a very low HER2 expression phenotype, for the eventual inclusion into our comprehensive cancer profiling solution. To date, studies with biomarker expression have been limited to tissue biopsy, which may not always yield contemporaneous sampling in the metastatic setting. These results offer a liquid biopsy test that might identify patients potentially responsive to HER2-directed therapies. Citation Format: Giuseppe Di Caro, David Bourdon, Andrew Kunihiro, Alessandra Cunsolo, Ernest Lam, Megan Slade, Martin Blankfard, Lee Schwartzberg. Development of a method to detect very low levels of HER2 expression in Circulating Tumor Cells (CTCs) by liquid biopsy in patients with metastatic breast cancer [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO5-04-04.

Abstract PO5-16-10: The efficacy of novel antibody-drug-conjugates on brain metastases in metastatic breast cancer patients – a multicenter real-world analysis

Abstract 15 – 30% of all patients with metastatic breast cancer (MBC) develop brain metastases (BMs). Treatment of BMs include radiation therapy and surgical resection while systemic treatment is challenging and prospective evidence for the treatment of active brain metastases is restricted to the small molecule Tucatinib. Recently, the antibody-drug-conjugates (ADCs) Sacituzumab-Govitecan (SG) and Trastuzumab-Deruxtecan (T-DXd) have shown to be highly effective in the treatment of triple-negative (SG), HER2-positive (T-DXd) and HR+/HER2- (SG and, in case of HER2-low-expression, T-DxD) MBC. However, there is only limited data, whether these macromolecules are also effective in patients with BMs. We therefore aimed to examine the efficacy of SG and T-DXd in patients with stable and active BMs in a multicenter real-world analysis. Female patients with stable or active BMs who were treated with either SG or T-DXd at the breast centers of Tuebingen University, Ulm University or Freiburg University in Germany before June 30, 2023 were included into this analysis. Data cut-off for this analysis was July 10, 2023. BMs were classified as active if they were newly diagnosed and did not require local treatment or if they were progressing and did not require local treatment. Preexisting BMs without intracranial disease progression or preexisting/newly diagnosed BMs that had been treated by surgery and/or radiotherapy directly prior to SG/T-DXd therapy were considered as stable. All patients underwent baseline magnetic resonance imaging (MRI) of the brain and received follow-up MRIs at least every three months. Growth dynamics of BMs were assessed by board certified neuroradiologists. Intracranial disease control rate (icDCR) was defined as the percentage of patients with at least intracranial stable disease at the first follow-up MRI. Intracranial progression-free survival (icPFS) was determined as the period between the first application of SG or T-DXd and intracranial disease progression or treatment cessation due to the patients’ will or the onset of intolerable toxicity. If ADC treatment was discontinued due to extracranial disease progression albeit at least stable intracranial disease patients were censored. Overall survival (OS) was defined as the period between the first application of SG or T-DXd and death. In total, 26 patients were included with a median of two prior therapy lines in the metastatic setting (range 2 – 15). 10 (38%) and 14 (54%) patients received SG and T-DXd, respectively. 2/26 (8%) patients receiving SG were consecutively subjected to T-DXd treatment. SG was applied to 12/12 patients (100%) due to triple-negative MBC and 12/16 patients (75%) treated with T-DXd were HER2-positive. The remaining 4/16 patients (25%) treated with T-DXd showed HER2 low tumor biology. 5/12 (42%) and 8/16 (50%) patients treated with SG or T-DXd had active BMs at treatment initiation. The icDCR was 33% (95% CI: 5% - 61%)/81% (95% CI: 62% - 100%) for all patients treated with SG/T-DXd and 40% (95% CI: 0% - 88%)/75% (95% CI: 43% - 100%) in case of active BMs. After a median follow-up of 7.2 months, 10/12 (83.3%) patients treated with SG and 4/16 (25%) patients subjected to T-DXd had discontinued treatment. Median icPFS was 3.1 months (95% CI: 0.4 – 5.8 months) for SG and not reached for T-DXd. 7/12 (58%) patients treated with SG and 4/16 patients (25%) treated with T-DXd died until data cut-off. Median OS was 7.2 months (95% CI: 3.0 – 11.4 months) for patients treated with SG and not reached for patients treated with T-DXd. SG and T-DXd showed promising clinical activity in both, stable and active cerebral breast cancer metastasis. Updated PFS and OS data will be reported at the meeting. Citation Format: Dominik Dannehl, Henning Schäffler, Tobias Engler, Lea Volmer, Arne Estler, Ilinca Popp, Stefanie Lorenz, Eva-Maria Grischke, Markus Hahn, Ghazaleh Tabatabai, Ingolf Juhasz-Böss, Wolfgang Janni, Sara Brucker, Florin-Andrei Taran, Andreas Hartkopf. The efficacy of novel antibody-drug-conjugates on brain metastases in metastatic breast cancer patients – a multicenter real-world analysis [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO5-16-10.

Abstract PO3-14-12: SIRT3 as a new potential predictive biomarker for response to CDK4/6 inhibition in ER+/HER2- metastatic breast cancer patients

Abstract Background: Several prospective, randomized clinical trials showed that the CDK4/6 inhibitor palbociclib in combination with either letrozole or fulvestrant significantly improves progression-free survival (PFS) in patients with ER+/HER2- metastatic breast cancer (MBC). However, in some cases, there is development of endocrine resistance and ultimate disease progression. Molecular analysis performed in tissue specimens collected in the PALOMA-3 study, comparing fulvestrant and Palbociclib versus fulvestrant placebo, demonstrated that one of the genes associated with an increased clinical benefit is SIRT3 (Sirtuin 3) which is thought to control mitochondrial integrity and metabolism (Cristofanilli M. et al., Lancet Oncol. 2016). This study aimed to evaluate in preclinical models the predictive role of SIRT3 in ER+/HER2- breast tumors. Methods: Using lentiviruses we generated MCF-7 and T47D cells stably expressing either control shRNA (sh ctr) or shRNA targeting SIRT3 (shSIRT3). With these models, we studied cell viability, tumor growth, apoptosis, and autophagy in MCF-7 cells treated with fulvestrant and palbociclib as a single treatment or in combination, these either alone or in combination with shSIRT3 (knockdown). Nude mice were used for our in vivo studies, and sh ctr or shSIRT3 MCF7 cells were injected. Results: We showed in vitro that the response to palbociclib was significantly associated with levels of SIRT3 expressionas high or low in ER+ cells (p< 0.0001). Furthermore, we found that irreversible cell growth inhibition mediates the beneficial effect of palbociclib in SIRT3 high expressing cellscompared to low expression (p< 0.001).Then, we evaluated the mechanistic activity of SIRT3. We showed thatSIRT3-low expression cells induced enhanced sensitivity to palbociclib by targeting the reactive oxygen species (ROS)/autophagy axis:(i) SIRT3 regulated the mitochondrial homeostasis (e.g. glucose, lactate, pyruvate, succinates), (ii) ROS levels where lower in sh crt comparing and shSIRT3 in treated and untreated cells (p< 0.001), (iii) in terms of senescence,a higher level of positive cells for β-gal activity was found (p≤0.05) and (iv) for autophagy, our western blot analysis showed cleaved LC3 proteins. Our in vivo studies showed that SIRT3 regulated treatment response to palbociclib with a significant decrease in tumor weight and tumor volume (p< 0.01) and importantly, after immunohistochemistry analysis, we validated the role of SIRT3 in regulating the proteins involved in the autophagy/senescence balance, was mainly in epithelial cells compared to stromal cells. Conclusion: Our preclinical studies demonstrated that elevated SIRT3 expression levels sensitizes ER+/HER2- breast tumors to palbociclib treatment. This study suggested that SIRT3 expression could represent a potential predictive biomarker in HR+ MBC patients treated with Palbociclib. Citation Format: Maroua Manai, Ghada Sahraoui, Raoudha Doghri, Lorenzo Gerratana, Paolo D’Amico, Youbin Zhang, Jeannine Donahue, Ami Shah, Carolina Reduzzi, Wenan Qiang, Massimo Cristofanilli. SIRT3 as a new potential predictive biomarker for response to CDK4/6 inhibition in ER+/HER2- metastatic breast cancer patients [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO3-14-12.

Abstract PO5-05-13: Clinical utility of whole body low dose computed tomography for detecting bone metastasis in breast cancer patients: A cross sectional study

Abstract Clinical utility of Whole Body Low Dose CT scan for detecting bone metastasis in Breast cancer patients: A cross sectional study Background: Skeletal scintigraphy (Bone scan) is the imaging of choice to detect bone metastasis in locally advanced and metastatic breast cancer patients. Nuclear medicine facilities are however limited in their availability. As an alternative diagnostic modality to bone scan, we studied the diagnostic capability of Whole-Body Low Dose CT (WBLDCT) scan for detection of bone metastasis in these patients. Materials and Method: This cross-sectional study was conducted from November 2021 to May 2023 at a tertiary healthcare center in India with an aim to study the clinical applicability of whole-body low dose computed tomography scan for detecting bone metastasis in patients with breast cancer. Breast cancer patients with primary tumor measuring 5cm or more, pathologically proven axillary lymph node metastasis, Stage III/IV disease, symptoms attributable to metastasis and suspected disease recurrence were included. All patients underwent WBLDCT and Bone scan within a period of about 2 weeks. WBLDCT was done during the same time as conventional dose CT scan was being done as part of metastatic workup. WBLDCT acquisition protocol was set in CT scan machine by modulating the technical parameters like Care dose 4D-automated, Care kV semi, rotation time & noise index. The image analysis was performed by Radiologist and Nuclear medicine experts in a blinded fashion. Data was recorded in MS Excel sheet. Sensitivity, specificity, positive and negative predicative value, and concordance rates were calculated using SPSS software ver 25.0. Agreement amongst WBLDCT and Bone scan was calculated using Inter-rater agreement. p value < 0.05 was taken as significant. Results: 110 patients were enrolled in this study. The mean age of participants was 48.5 years and three fourth had stage III disease at presentation. Estrogen receptor positive disease was seen in 43.64% participants while 30% were triple negative. Her2neu positive disease was seen in 27.27% patients. Bone scan couldn’t be done in 03 patients who deferred treatment (these had no bone metastasis on WBLDCT). Both bone scan and WBLDCT detected bone metastasis in 19 patients. Bone scan picked up additional metastasis in three patients which were missed on WBLDCT. WBLDCT detected bone metastasis additionally in three patients which were not detected on Bone scan. Multiple lesions were most seen in vertebrae in 38.5% and 28.6% on bone scan and WBLDCT respectively. The sensitivity and specificity of WBLDCT for detection of bone metastasis was 86.36% and 96.47% respectively. The concordance rate between Bone scan and WBLDCT scan was 94.39% with an Inter-rater Kappa(k) quotient for agreement of 0.828 (p< 0.0001). Conclusion: WBLDCT scan has comparable diagnostic capability to skeletal scintigraphy in detecting bone metastasis in breast cancer and may be a useful alternative specially in resource limited settings. Table 1: Sensitivity, specificity, positive predictive value and negative predictive value of WBLDCT for detection of metastasis Variables Values Sensitivity (95% CI) 86.36% Specificity (95% CI) 96.47% AUC (95% CI) 0.91 Positive Predictive Value (95% CI) 86.36% Negative Predictive Value (95% CI) 96.47% Diagnostic accuracy 94.39% Inter-rater agreement (kappa) 0.828 Citation Format: Lipton Mitra, Suhani Suhani, Ankur Goyal, Rakesh Kumar, Mohit Joshi, Hemanga Bhattacharjee, Haresh KP, Raju Sharma, Rajinder Parshad. Clinical utility of whole body low dose computed tomography for detecting bone metastasis in breast cancer patients: A cross sectional study [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO5-05-13.

Abstract PO4-07-11: FDG-PET is superior to bone scintigraphy for the detection of bone metastases in breast cancer patients

Abstract Background: Bone is the commonest site for metastases in breast cancer patients, with up to 44% of patients having bone as their sole site of metastatic disease. Patients are at increased risk of morbidity from skeletal related events (SRE) from bone metastases due to pathological fractures and spinal cord compression. Early diagnosis is crucial so that bone modifying agents can be used to prevent SREs and other agents such as CDK4/6 inhibitors can be considered. Bone scintigraphy is the most widely performed first investigation for patients at high risk or symptomatic from bone metastases. Methods: We performed a meta-analysis comparing FDG-PET and bone scintigraphy using PubMed, Science Direct, and Embase for the literature search. 1009 patients were included in the study. Data for 2 × 2 contigency tables was selected and QUADAS-2 was used for quality assessment. Diagnostic accuracy was performed using Graph pad Prism 9.5.1 and R studio 2022. Pooled sensitivity and specificity of FDG-PET/CT was 96.6% (95% CI=91.5%-98.7%) and 96.8% (95% CI=82.1%-99.5%) respectively. Respective results for BS were 88.3% (95% CI=79.8%-93.5%) and 81.3% (95% CI=63.1%-91.7%). Sensitivity and specificity of FDG-PET/CT was significantly higher than BS (P=0.0063, P= 0.0068, respectively). The diagnostic odds ratio and area under ROC curve were significantly higher for FDG-PET/CT than BS (654.36 vs 35.24, and 0.980 vs 0.877, respectively). Conclusion: FDG-PET is superior to bone scinitigaphy for the detection of bone metastases in breast cancer.The benefits of replacing BS with FDG-PET/CT are evident. However othere technologies such as DW-MRI should be considered. Large multicentre prospective trials with strict FDG-PET/CT imaging protocols compared to DW-MRI both for disease detection and monitoring of response are required to strengthen the evidence in this field, to help inform imaging guidelines and best practices in the future. Newer technologies such as [18F]estradiol (FES)-PET and [18F]GE-226 for HER2 expression also warrant further investigation in ER positive and HER2 positive breast cancer. Citation Format: Laura Kenny, Maisher Tin-U. FDG-PET is superior to bone scintigraphy for the detection of bone metastases in breast cancer patients [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO4-07-11.

Abstract PO3-22-07: Predicting Additional Axillary Metastases in Breast Cancer Patients with Positive Targeted Axillary Dissection Lymph Nodes after Neoadjuvant Treatment

Abstract Background: Neoadjuvant chemotherapy (NACT) is increasingly used for axillary downstaging in clinically node-positive breast cancer patients, and a considerable proportion achieves axillary pathological complete response (ax-pCR). After NACT, axillary staging can be done by targeted axillary dissection (TAD). In case of metastases at TAD, axillary lymph node dissection (ALND) is offered regardless of metastases size. This contrasts primary surgery, where small sentinel node metastases (ypN0(i) and ypN1mi) and ≤2 positive sentinel nodes do not confer ALND, although a proportion of patients with small metastases have additional metastatic lymph nodes (LNs) in the axilla. So far, the residual metastatic burden in the axilla when TAD LNs are positive after NACT is unknown. If subgroups of patients with low residual metastatic burden in the axilla (non-TAD LNs) could be identified, these subgroups may be offered de-escalated axillary treatment. Therefore, we investigated the risk of residual metastatic burden in the axilla when the TAD LNs harbored metastases. Methods: We retrospectively retrieved DBCG data on patients staged by TAD after NACT in Denmark between 1.1.2016-31.8.2021. We registered: age, breast biopsy date, type of surgery, type of axillary surgery, count of LNs, sentinel nodes, and marked lymph nodes with and without metastases, including metastasis size, breast tumor histology and receptor subtype, breast tumor size at diagnosis and in the surgical specimen, malignancy grade and type of neoadjuvant treatment. We excluded patients with inflammatory breast cancer, < 4/>8 cycles of NACT, or a non-standard NACT regimen. The primary outcome was risk factors for having high ( >3), low (1-3), or no residual metastatic burden in the axilla when the TAD LNs harbored metastases. We modeled risk factors for both high and low residual metastatic burden in the axilla using multivariable logistic regression and constructed risk models based on the regression coefficients. Results: We identified 1626 patients receiving NACT and TAD in the inclusion period. After excluding ineligible patients and patients who achieved ax-pCR with no subsequent ALND (46%), the study included 383 patients with positive LNs at TAD for further analysis: thereof 188, 127, and 68 with 0, 1-3 and >3 positive non-TAD LNs, respectively. In the adjusted logistic regression analysis, we found that breast pCR (OR= 0.06, 95% CI < .01-0.41, p < .001) and a low proportion of positive TAD LNs (0-66% vs >66%) (OR=0.32, 95% CI 0.17-0.58, p = < .001) were associated with low risk of high residual metastatic burden in the axilla. Patients with one or both low-risk factors present had an 8% (14 of 176 patients) risk of high residual metastatic burden in the axilla. The predictive value of the model for having < 3 non-TAD LN metastases was 92%. When analyzing the 315 patients with ≤3 positive non-TAD LNs, the adjusted logistic regression analysis of 1-3 vs 0 positive non-TAD LNs showed that ypN0(i) in the TAD LN (OR=0.14, 95% CI 0.04-0.53, p = 0.002), small tumor size at diagnosis (20-49 mm vs ≥ 50 mm) (OR = 0.29, 95% CI 0.14-0.60, p = 0.002), breast pCR (OR= 0.38, 95% CI 0.15-0.98, p = 0.04) and low proportion of positive TAD LNs (33-66% vs >66%) (OR= 0.46, 95% CI 0.27-0.77, p = 0.01) were associated with no residual metastases in the axilla. Using these risk factors, 19% (11/58) of the patients in the lowest risk quartile had further metastatic spread to the axilla. Conclusion: Based on an extensive breast cancer registry, we find that breast pCR, low proportion of positive TAD LNs, small metastases, and small tumor size are associated with low risk of residual metastatic LNs in the axilla when the TAD LNs are positive after NACT. With these risk factors, we propose two models to identify patients with low non-TAD residual metastatic burden and patients with a high likelihood of no further metastases. The models can guide breast surgeons in de-escalating axillary treatment in these groups. Citation Format: Frederikke Munck, Maj-Britt Jensen, Ilse Vejborg, Maria Gerlach, Maja Maraldo, Niels Kroman, Tove Tvedskov. Predicting Additional Axillary Metastases in Breast Cancer Patients with Positive Targeted Axillary Dissection Lymph Nodes after Neoadjuvant Treatment [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO3-22-07.

Abstract PO5-18-04: Effect of Digoxin on clusters of circulating tumor cells in patients with metastatic breast cancer (DICCT)

Abstract Background: The presence of circulating tumor cell (CTC) clusters is associated with tumor progression and with a bad prognosis in various cancer types1,2. In breast cancer, a pre-clinical model demonstrated that Na/K-ATPase inhibitors such as digoxin could dissolve CTC clusters and reduce metastasis3. DICCT is a single-arm, therapeutic exploratory phase I study aimed to examine whether digoxin can disrupt CTC clusters in metastatic breast cancer patients (NCT03928210). Material and methods: Metastatic breast cancer patients in whom clusters of CTCs have been detected were eligible. Patients with concomitant heart disease were excluded. After progressive disease in any line of therapy, a window of opportunity before initiation of subsequent systemic therapy was used to administer digoxin treatment for seven (7) days. For CTC detection, blood samples were processed with the FDA-cleared Parsortix system (ANGLE plc, UK). Captured CTCs were stained for EPCAM, HER2, EGFR (positive CTC selection) and CD45 (exclusion marker). To gain insight into the cluster-dissolution ability of digoxin, the primary endpoint was size of CTC clusters (i.e. number of cells within each cluster) under digoxin therapy. The cumulative effect of digoxin treatment on the primary endpoint was assessed by a linear regression model. Results: Nine (9) patients with CTC clusters detected at baseline were enrolled. A target level of digoxin above 0.7 ng/ml could be confirmed at day 7 for all patients. For quantitative and qualitative analysis of CTC clusters, 5.5 to 27 ml of blood were analyzed at baseline, at day 0 pre-treatment, and post 2 hours, 3 days and 7 days of digoxin treatment. The average cluster size ranged between 2 and 11.8 cells (median 2.9) considering all samples from all patients. Digoxin treatment reduced cluster size in 8 patients (88.9%) to different extents, and the proportion of CTC cluster over single CTCs was also reduced in 6 patients (66.7%). The effect of digoxin was evident in both homotypic (cancer cells only) and heterotypic (aggregates of CTCs and white blood cells) clusters. The treatment was well tolerated, and no adverse events related to the study treatment occurred. All patients completed the treatment according to the protocol. Conclusion: DICCT provides the first-in-human proof-of-principle that digoxin induces a partial dissolution of CTC clusters in patients with metastatic breast cancer at drug levels that are safe and well tolerated. Conceptualization of follow-up trials including Na/K-ATPase inhibitors and patient outcome endpoints are underway.

Abstract PO3-06-01: Factors associated with first- and second- line attrition among metastatic breast cancer patients

Abstract Background: Estimating patient attrition across lines of treatment, i.e., the probability that upon failing one treatment the patient will be able to receive a subsequent treatment, may be a valuable tool for treatment sequencing. We sought to describe first-to-second line (1to2-line) and second-to third line (2to3-line) attrition rate and factors associated with attrition. Methods: The GIM14/BIO-META is an ongoing, ambispective observational multicenter study enrolling breast cancer patients receiving first-line therapy. In progressing patients, attrition was defined as no further anticancer treatment and death within 6 months from the end of the previous line. Attrition from 1to2-line and from 2to3-line was studied by descriptive analyses, factors associated with attrition by univariate ad multivariable logistic models. Results: From January 2000 to December 2021, 3,109 patients with metastatic breast cancer were enrolled in the GIM14/BIO-META study. After the exclusion of 611 patients with ongoing first-line treatment, we included 2,498 patients in the analysis of 1to2-line attrition. Considering tumor subtype, 1,650 (66.0%) patients were diagnosed with metastatic luminal-like, 622 (24.9%) with HER2-positive and 177 (7.1%) with triple negative (TN) tumors. At the time of diagnosis of advanced disease, almost half of the patients (52.0%) had only one involved metastatic site and 45.9% of the patients were diagnosed with visceral involvement. Overall, 1to2-line attrition was 9.0% (224/2,498) with similar attrition for patients with luminal-like (8.5%) and HER2-positive (7.1%) breast cancer. Patients with TN disease experience the highest 1to2-line attrition (13.0%). Age, disease-free interval from primary tumor diagnosis, and type of metastatic spread independently predicted 1to2-line attrition. Univariate analyses of factors associated with 1to2-line attrition among patients with luminal-like breast cancer were similar to those of the entire cohort. Overall, 2to3-line attrition was 14.0% (260/1,861) with higher attrition rates among patients with TN disease (22.7%) compared to patients with luminal-like (13.4%) and HER2-positive (13.0%) breast cancer. Age, tumor subtype, pattern of visceral spread and shorter time-to treatment discontinuation during first-line therapy were independent factors associated with 2to3-line attrition. Conclusions: Pending confirmation in independent series and integration with biomarkers of treatment failure, these results, may provide a valuable support for treatment decisions and clinical research on treatment sequencing. Citation Format: Eva Blondeaux, Luca Boni, Giovanna Chilà, Arianna Dri, Roberta Caputo, Francesca Poggio, Alessandra Fabi, Grazia Arpino, Federico Pravisano, Elena Geuna, Tommaso Ruelle, Irene Giannubilo, Michelino de Laurentiis, Fabio Puglisi, Claudia Bighin, Matteo Lambertini, Filippo Montemurro, Lucia Del Mastro. Factors associated with first- and second- line attrition among metastatic breast cancer patients [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO3-06-01.

Abstract PO3-06-05: Association of tumor-derived extracellular vesicles with circulating tumor DNA alterations in metastatic breast cancer patients: exploring differences in inflammatory breast cancer

Abstract Background: Liquid biopsy provides a real-time assessment of metastatic breast cancer (MBC). Recently, the complementary prognostic value of tumor-derived extracellular vesicles (tdEVs) and circulating tumor cells (CTCs) has been reported. We have previously confirmed the strong prognostic significance of CTCs and tdEVs in inflammatory breast cancer (IBC). While previous studies have reported the association of CTCs with circulating tumor DNA (ctDNA) alterations in MBC, no evidence is available for tdEVs. This study aimed to analyze the association of tdEVs with ctDNA alterations, to investigate the molecular pathways underlying their presence. Moreover, we explored potential differences of this association in patients (pts) with IBC to provide a comprehensive liquid biopsy-based portrait of this aggressive subtype of BC. Methods: Blood samples were collected from 355 pts with MBC before starting a new line of therapy at Northwestern University (Chicago, IL) between 2016 and 2021 (NU16B06 trial). For CTCs and tdEVs analysis, 7.5 mL of blood was processed with the CellSearch® system. The ACCEPT software was applied to CellSearch® images to automatically enumerate CTCs and tdEVs. Positivity cutoff was ≥5 for CTCs, while tdEV cutoff points were < 20 (low), 20-79 (intermediate), and ≥80 (high). For ctDNA analysis, matched plasma samples (± 1 month) were analyzed with the Guardant360™ NGS platform for the detection of somatic single nucleotide variants (SNVs) and copy number variations (CNVs), which were classified into oncogenic pathways based on defined profiles generated on the Cancer Genome Atlas database (p53, PI3K, ER, RTK, RAS, RAF, WNT, MYC, cell cycle, notch). Associations between ctDNA pathways alterations and tdEVs were tested in the overall population by multinomial logistic regression and corrected for significant clinical characteristics. Differences in liquid biopsy features between IBC and non-IBC subgroups were analyzed through Fisher's exact test. Results: Of the 355 MBC pts, 210 (62%) had HR+ BC, 61 (17%) had HER2+ BC, and 68 (20%) had triple-negative BC. Eighty-three (23%) had a diagnosis of IBC and had a numerically lower tdEV count. Also, lower tdEVs were detected in HER2+ BC as compared with HR+. Significantly higher tdEVs were observed among pts with lobular histology, liver, and bone metastases. CTC count was significantly associated with tdEV number. A matched plasma sample for ctDNA analysis was available for 175 pts (62 IBC and 113 non-IBC). In the overall population, SNVs in ER pathway were associated with intermediated/high levels of tdEVs (p=0.004 and 0.008). A similar association was observed for CNVs in the cell cycle pathway (p=0.008 and 0.007). Moreover, associations with ≥80 tdEVs were observed for PI3K SNVs and CNVs (p=0.039 and 0.004, respectively), RTK CNVs (p=0.023), and MYC CNVs (p=0.001). In multivariable analysis, clinical characteristics associated with higher tdEVs were lobular histology (p=0.014 for 20-79 and < 0.001 for ≥80) and bone metastases (p=0.019 for 20-79 and 0.002 for ≥80). When considering clinical variables of interest, only ER SNVs and MYC CNVs were significantly associated with intermediate (p=0.031) and high (p=0.022) tdEV counts, respectively. While the association with ER SNVs and cell cycle CNVs was significant both in the IBC and non-IBC subgroups, others were specific for a certain subgroup: higher tdEVs were significantly associated with PI3K SNVs only in non-IBC pts whereas the significant association with CNVs in PI3K and MYC pathways was observed only in pts with IBC. Conclusion: Detection of tdEVs was associated with particular genomic profiles. These alterations seem to be different in IBC further underlying a different biology of this BC subtype. Additional studies are needed to explore how to integrate different liquid-biopsy based biomarkers in the management of pts with MBC. Citation Format: Eleonora Nicolò, Lorenzo Gerratana, Lorenzo Foffano, Laura Munoz Arcos, Mara Serena Serafini, Maroua Manai, Letizia Pontolillo, Nadia Bayou, Elisabetta Molteni, Amanda Kaylan Strickland, Youbin Zhang, Paolo D’Amico, Andrew Davis, Jeannine Donahue, Huiping liu, William Gradishar, Ami Shah, Giuseppe Curigliano, Carolina Reduzzi, Massimo Cristofanilli. Association of tumor-derived extracellular vesicles with circulating tumor DNA alterations in metastatic breast cancer patients: exploring differences in inflammatory breast cancer [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO3-06-05.

Abstract PO1-17-05: Real-world effectiveness of palbociclib plus aromatase inhibitors (AI) in metastatic breast cancer patients with cardiovascular diseases

Abstract Background Breast cancer survivors are at risk for mortality from cardiovascular diseases (CVD). CVD and their treatments can impact breast cancer treatment selection and clinical outcomes. A cyclin dependent kinase 4/6 inhibitor (CDK4/6i) combined with endocrine therapy (ET) is more effective than ET alone for hormone receptor-positive/human epidermal growth factor receptor 2-negative (HR+/HER2) metastatic breast cancer (MBC). CDK4/6i plus ET is now the standard of care in the first-line setting for HR+/HER2 MBC. However, data on the effectiveness of CDK4/6i in MBC patients with CVD are limited. We compared overall survival (OS) and real-world progression-free survival (rwPFS) of palbociclib plus AI (PAL+AI) vs AI alone in HR+/HER2 MBC patients with CVD in routine US clinical practices. Methods The Flatiron Health longitudinal database contains electronic health records from >280 cancer clinics, representing >3 million actively treated cancer patients in the US. Using the Flatiron database, we conducted a retrospective analysis of 469 patients with HR+/HER2 MBC and CVD who started PAL+AI or AI as first-line therapy between February 2015 and March 2020. CVD prior to the initiation of PAL+AI or AI were identified based on their definitions within the National Cancer Institute-Comorbidity Index (NCI-CI), including myocardial infarction, congestive heart failure, peripheral vascular diseases, and cerebrovascular diseases. Patients were assessed from start of PAL+AI or AI to September 30, 2020 (data cutoff date), death, or last visit, whichever came first. OS was defined as months from start of PAL+AI or AI to death. rwPFS was defined as months from start of PAL+AI or AI to death or disease progression, evaluated based on clinical assessment or radiographic scan/tissue biopsy. Stabilized inverse probability treatment weighting (sIPTW) as primary analysis was used to balance baseline demographics and clinical characteristics. Cox proportional-hazards models were used to estimate the relative effectiveness of PAL+AI vs AI alone. Results Of the 469 eligible patients, 160 (34.1%) were treated with PAL+AI and 309 (65.9%) were treated with AI alone. Compared with AI-alone patients, those treated with PAL+AI were younger and were more likely to have de novo MBC, ≥2 metastatic sites, and lung/liver involvement. After sIPTW, patient characteristics were generally balanced. After sIPTW, median OS (95% confidence interval [CI]) was 40.7 months (30.956.0) in PAL+AI patients and 26.5 months (23.337.3) in AI patients (hazard ratio [HR]=0.732, 95% CI=0.5370.997, p=0.0476). Median rwPFS (95% CI) was 20.0 months (11.7–27.5) in PAL+AI patients and 12.5 months (9.718.3) in AI patients (HR=0.679, 95% CI=0.5120.900, p=0.0070). Consistent results were observed with multivariate Cox proportional-hazards models as sensitivity analysis. See Table for baseline patient characteristics and outcome results. Conclusions First-line PAL in combination with AI is associated with prolonged OS and rwPFS in patients with HR+/HER2 MBC and CVD in a real-world setting compared with AI alone. Further studies with larger cohorts and comprehensive assessments of comorbidities are needed to provide additional evidence of outcomes and safety of CDK4/6i plus AI for MBC patients with various comorbid conditions in routine clinical practice. Citation Format: Adam Brufsky, Xianchen Liu, Benjamin Li, Lynn McRoy, Connie Chen, Doris Makari, Rachel Layman, Hope Rugo. Real-world effectiveness of palbociclib plus aromatase inhibitors (AI) in metastatic breast cancer patients with cardiovascular diseases [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO1-17-05.

Abstract PS15-04: A Phase 1b/2 study of palazestrant (OP-1250), an oral complete estrogen receptor antagonist (CERAN) and selective ER degrader (SERD), with palbociclib in ER-positive, HER2-negative, advanced or metastatic breast cancer patients

Abstract Background: Palazestrant (OP-1250) is a small molecule oral complete estrogen receptor (ER) antagonist (CERAN) and selective ER degrader (SERD) that binds the ligand binding domain of ER and completely blocks ER-driven transcriptional activity in both wild-type (ESR1-wt) and mutant (ESR1-mut) forms of ER. In preclinical studies, palazestrant demonstrated improved tumor growth inhibition and shrinkage when combined with a cyclin-dependent kinase 4/6 (CDK4/6) inhibitor. In a Phase 1/2 monotherapy clinical study in patients with ER-positive, human epidermal growth factor receptor 2-negative metastatic breast cancer, palazestrant was well tolerated with demonstrated antitumor efficacy and favorable pharmacokinetics (PK) supporting once a day (qd) dosing at the recommended Phase 2 dose of 120 mg. In this study, pts received palazestrant at escalating doses of 30, 60, 90, and 120 mg qd in combination with palbociclib (125 mg qd) and no dose-limiting toxicities were observed. Palazestrant did not affect palbociclib PK and no drug–drug interactions (DDIs) occurred. Here we report updates on safety, efficacy, and PK from the ongoing study of palazestrant in combination with palbociclib. Methods: Patients with advanced or metastatic breast cancer with progression on or after ≤1 line of endocrine therapy (prior CDK4/6 inhibitor therapy and ≤1 chemotherapy allowed) were enrolled to receive oral palazestrant 120 mg qd with oral palbociclib 125 mg qd for 21 of 28 days (NCT0526610). Results: As of May 12, 2023, 33 patients have been treated with palazestrant in combination with palbociclib; 12 pts were dosed in the dose-escalation phase and 21 patients were dosed in the dose-expansion phase of the study. Twenty-two patients (67%) received prior CDK4/6 inhibitor therapy; 15 patients received prior palbociclib. Thirteen of 25 patients (52%) with available baseline ctDNA had an ESR1 mutation. The most common (≥20%) treatment-emergent adverse events (TEAEs) were neutropenia, nausea, vomiting, constipation, and diarrhea. Most of these events were grade 1 or 2. The most common grade 3 or 4 related AE was neutropenia (18/33 [55%] were grade 3; 3/33 [9%] were grade 4). The steady-state exposure of palazestrant when dosed with 125 mg palbociclib was consistent with the monotherapy study. Palbociclib exposure at steady-state was comparable to published monotherapy data when combined with palazestrant at all dose levels tested. As of the data cut-off, there were 4 partial responses (2 confirmed) out of 19 response-evaluable patients, with a clinical benefit rate (CBR) of 42% (8/19) across all patients and 67% (6/9) in patients with ESR1 mutations. Conclusions: Palazestrant and palbociclib dosed in combination were well tolerated with a safety profile consistent with the individual profiles of each drug as monotherapy, and there were no DDIs. Tumor responses and clinical benefit were observed in this population of patients, including those who received prior CDK4/6 inhibitors. Expanding on our previous report, these data provide the rationale to continue advancing the clinical development of palazestrant with the approved dose of palbociclib. Updated data will be presented. Citation Format: Arlene Chan, Daphne Day, Phuong Dinh, Michael Slancar, Janine Lombard, Vinod Ganju, Nicole McCarthy, Rosalind Wilson, Demiana Faltaos, Gurpreet Mathauda-Sahota, Caitlin Murphy. A Phase 1b/2 study of palazestrant (OP-1250), an oral complete estrogen receptor antagonist (CERAN) and selective ER degrader (SERD), with palbociclib in ER-positive, HER2-negative, advanced or metastatic breast cancer patients [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PS15-04.

Abstract PO5-05-07: Efficacy and safety of first line CDK4/6i plus endocrine therapy for patients with HR+/HER2- metastatic breast cancer:initial real-world experience at Ho Chi Minh city oncology hospital, Viet Nam

Abstract Background The cyclin-dependent kinases (CDK)4/6 inhibitors (CDK4/6i) palbociclib and ribociclib have been available in Viet Nam since 2021 for the treatment of hormone receptor-positive metastatic breast cancer (MBC). Data regarding CDK4/6i benefit in Vietnamese MBC are sparse. This study evaluated the impact of CDK4/6i in first-line HR+/HER2− MBC using real-world experience at Ho Chi Minh City Oncology Hospital. Methods A single-institution study analyzed retrospective data from 108 patients treated with palbiciclib or ribociclib with endocrine therapy in first-line in HR+/HER2– MBC patients at Ho Chi Minh city oncology hospital. Patient characteristics, PFS, treatment response, and toxicity profiles were analyzed. Results Baseline patients’ characteristics are detailed in Table 1.The median follow-up was 12.5 months (95% CI: 10.9-13.3). Best responses by the line of therapy are in Table 2. The median PFS has still not been reached. The PFS rates at 6, 12 and 18 months were 94.4%, 93.5% and 91.5%, respectively. Patients with bone-only metastasis have a better PFS than visceral metastasis (p = 0.059). Patients with recurrent disease had shorter PFS (p = 0.083) than those presenting with de novo metastasis. The most common reasons for toxicity were neutropenia (92.6%), anemia (35.2%), thrombopenia (22.2%) and the incidence of diarrhea was only 2,8%. None were related to QTc-prolongation Conclusion The real-world effectiveness and safety with CDK4/6 inhibitors in our institution HR+/HER2– MBC patients mimics that observed in the clinical trials. This finding supports the use of CDK4/6i in combination with endocrine therapy as standard of care for HR+/HER2- MBC in Viet Nam. The study also suggests the need for more study of under-represented minority populations. Further studies are ongoing to validate these findings incorporating additional cancer centers. Keywords: advanced/metastatic breast cancer, Asia, CDK4/6 inhibitors, real world Table 1. Patient Demographics and Baseline Disease Characteristics (N=108) Characteristics N (%) Age, y: Median 52 Stage Recurrent from earlier stage, stages 0–III 67 (62) De novo, newly diagnosed stage IV at enrolment 41 (38) DFI < 12 months 5 (4.6) 12-24 months 12 (11.1) > 24 months 51 (47.2) No. of metastatic sites 1 49 (45.4) 2 37 (34.3) ≥ 3 22 (20.4) Metastasis pattern Bone only 30 (27.8) Other 78 (72.2) CDK4/6i Palbociclib 35 (32.4) Ribociclib 73 (67.6) Partner ET AIs 94 (87) Fulvestrant 14 (13) Table 2. Best responses of therapy (N=108) Best responses (N,%) CR 2 (1.9) PR 29 (26.9) SD 67 (62.1) PD 10 (9.3) Total 108 (100) ORR 31 (28.8) CBR 76 (70.3) Table. Citation Format: Hoang-Quy Nguyen, Hong-Duc Phan-Thi, Thi-Hong-Van Le. Efficacy and safety of first line CDK4/6i plus endocrine therapy for patients with HR+/HER2- metastatic breast cancer:initial real-world experience at Ho Chi Minh city oncology hospital, Viet Nam [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO5-05-07.

Abstract PO4-04-06: Exploring the use of tyrosine kinase inhibitors (TKIs) in the management of HER2-positive metastatic breast cancer post trastuzumab emtansine (T-DM1) therapy failure: Insights from a real-world study

Abstract Background Trastuzumab emtansine (T-DM1) is the established standard second-line treatment for HER2-positive metastatic breast cancer (MBC) patients who have previously received trastuzumab. However, there is ongoing debate regarding the subsequent therapeutic options following T-DM1 failure. This study aimed to evaluate the efficacy and safety of tyrosine kinase inhibitors (TKIs)-based therapy in HER2-positive MBC patients with resistance to T-DM1. Methods During the period from September 2018 to October 2021, a multicenter real-world study was conducted, enrolling a total of 53 patients diagnosed with HER2-positive metastatic breast cancer (MBC). These patients underwent TKIs-based therapy following the failure of T-DM1 treatment. The primary focus of the study was on evaluating progression-free survival (PFS) as the main endpoint. Secondary endpoints encompassed objective response rate (ORR), overall survival (OS), clinical benefit rate (CBR), and safety assessments. Results A total of 53 patients received TKIs-based therapy as a second-line or later treatment. The median progression-free survival (PFS) for TKIs-based therapy was 11.9 months (95% CI 7.9-15.9). The objective response rate (ORR) and clinical benefit rate (CBR) were found to be 19.6% and 72.5%, respectively. Among patients with brain metastasis (n=12), a median PFS of 10.5 months (95% CI 7.5-13.5) and an intracranial ORR of 33.3% were observed. Patients treated with pyrotinib (n=21) showed improved PFS compared to those treated with lapatinib (n=30), as well as patients who had derived favorable benefit from T-DM1 (PFS ≥ 6 months). Hormone receptor status (HR) and response to T-DM1 were identified as independent factors affecting the effectiveness of TKIs-based therapy. The most frequently reported adverse events included thrombocytopenia (23.6%), diarrhea (15.7%), leucopenia (15.7%), and hand-foot syndrome (15.7%). Conclusion TKIs-based therapy demonstrated favorable effectiveness and safety in HER2-positive metastatic breast cancer (MBC) patients who had previously received T-DM1 but experienced treatment failure. This includes patients with brain metastases. Notably, individuals who derived favorable benefits from prior T-DM1 treatment displayed significantly prolonged progression-free survival (PFS) when undergoing subsequent TKIs-based therapy. Citation Format: Yongmei Yin, Chunxiao Sun, Yijia Hua, Nan Jin, Wei Li, Xiang Huang. Exploring the use of tyrosine kinase inhibitors (TKIs) in the management of HER2-positive metastatic breast cancer post trastuzumab emtansine (T-DM1) therapy failure: Insights from a real-world study [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO4-04-06.

Abstract PO4-05-05: Immune Activation Signatures for predicting CDKi primary response in advanced breast cancer patients

Abstract Background Cyclin Dependent Kinase inhibitors (CDKi’s) in combination with Endocrine Therapy (ET) have changed the first line management of patients with the most common subtype (HR+, HER2-) of metastatic breast cancer (MBC), improving progression-free survival (PFS) and overall survival. However, in approved indications for advanced breast cancer, approximately 20% of patients have been observed to have no response to CDKi’s and ET, and to progress after starting these therapies. Unlike other targeted therapeutics, there is no companion diagnostic or other clinically reliable biomarker for clinical decision support to indicate which patients will and will not benefit from CDKi therapy. Methods We have developed a novel platform that measures the Immune Activation Signature of patient plasma samples. Via simple measurements of the total concentration of protein-incorporated amino acid residues within patient plasma samples, the platform is designed to reveal changes in the proportion of immunoglobulins and albumin, and class-switching among immunoglobulins. For that purpose, we use Bioorthogonal chemical labelling reactions to label the protein-incorporated amino acids residues within the plasma. We measured the plasma samples of N=30 HR+, HER2- MBC patients, median age 54 years old, who were baseline naïve for CDKi’s treatment (16 on palbociclib, 11 on ribociclib, and 3 on abemaciclib) and ET. Eighteen patients had metastatic visceral disease and 12 patients had bone-only MBC. All patients were prospectively followed, and response assessed according to RECIST criteria on a CT scan every 3-months. Results Non-responding patients developed objective progressive disease during the first 6 months after starting CDKis and ET. In this cohort, 4 patients (13%) were classified as non-responders. The median PFS in non-responding patients was 4.5 months (4.03-5.02) and the median PFS in the cohort of responding patients was 16.6 months (6.8 – 40.9). The Immune Activation Signatures of the Responding and Non-Responding patients are shown in table 1. We analyzed the results with classical statistics and machine learning. A multivariate analysis of variance (MANOVA) test of the null hypothesis that the Immune Activation Signatures of Non-Responders and Responders are the same gave p = 0.00388. We analyzed the measured Immune Activation Signatures using a supervised machine learning classifier and observed in a held-back validation set correct prediction of 100% of non-responding patients and 95% accurate predictions overall. Conclusions According to these results, this platform may provide a clinically helpful biomarker for clinical decision support in the advanced or aggressive breast cancer context (patients with visceral metastasis bordering on visceral crisis), or for patient stratification in new indications. Table. Immune Activation Signature measurements (mean values in Clinical Outcome) Citation Format: Luis Costa, Cong Tang, Emma Yates, Qi Shi, Wesley Sukdao, Patricia Corredeira, Gonçalo Costa, Helena Pais, Catarina Abreu, Leonor Ribeiro, Rita Teixeira de Sousa, Sofia Torres, André Mansinho, Sandra Casimiro, Ana Cavaco, Patricia Alves, Angela Rodrigues, Lisiana Szeneszi, Gonçalo Bernardes. Immune Activation Signatures for predicting CDKi primary response in advanced breast cancer patients [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO4-05-05.

Abstract PO4-27-06: Design of Active Phase 3 ENABLAR-2 Study Evaluating Enobosarm +/- Abemaciclib in Patients with AR+ER+HER2- 2nd-Line Metastatic Breast Cancer Following Tumor Progression on an Estrogen Blocking Agent Plus Palbociclib or Ribociclib

Abstract Background: Targeting the androgen receptor (AR) with an oral selective agonist, enobosarm, is a novel approach to overcome ER and CDK4/6 resistance to suppress metastatic breast cancer (mBC). Preclinical studies in CDK4/6 inhibitor and estrogen blocking agent resistant PDX mBC models demonstrated that enobosarm alone or in combination with another CDK 4/6 inhibitor suppressed PDX mBC growth. In a subgroup analysis from a Phase 2 study, enobosarm demonstrated efficacy in the treatment of AR+ ER+ HER2- metastatic breast cancer in patients who had tumor progression on estrogen blocking agent and a CDK 4/6 inhibitor with a best overall response rate of 30% (2CRs and 1 PR). A Phase 3 ENABLAR-2 multi-center, open label, study evaluating enobosarm +/- abemaciclib is open and active for the treatment of HR+HER2- mBC. Methods: The two-staged Phase 3 ENABLAR-2, open-label, randomized, multicenter study is being conducted in AR+ER+ HER2- 2nd-line mBC who have progressed on estrogen blocking agent plus palbociclib or ribociclib. In the Stage 1 of the study (160 patients), five treatment arms will be assessed with the primary efficacy endpoint of ORR: enobosarm 9 mg QD, enobosarm 1 mg QD + abemaciclib, enobosarm 3 mg QD + abemaciclib, enobosarm 9 mg QD + abemaciclib, and an estrogen blocking agent, active control (a nonsteroidal AI, exemestane +/- everolimus, or SERD). Secondary efficacy endpoints include progression-free survival (PFS). In Stage 2 of the study, patients will be randomized to receive enobosarm +/- abemaciclib (based on outcome of ORR in Stage 1) or estrogen blocking agent, active control, with the primary endpoint of PFS and secondary efficacy endpoints including, ORR, CBR, OS, as well as changes in quality-of-life measurements (SPPB, EORTC-QLQ, body composition measured by DEXA). Randomization will be stratified by AR% nuclei staining and by line of treatment for metastatic disease. Subjects will receive study drug until disease progression is observed. Preliminary Results: To date, 3 patients have been treated with enobosarm 9 mg in combination with abemaciclib. The combination therapy was well tolerated with no new safety findings. There were no drug-drug interactions between enobosarm and abemaciclib. Two patients have achieved BOR of a partial response with up to 79% and 56% reduction in their target lesion recorded by local reads on day 224 post-treatment initiation (PTI). The third patient has achieved a stable disease and continues to receive treatment (on study 10+ months). Conclusions: Preliminary data of efficacy and safety of enobosarm in combination with abemaciclib are encouraging. The Phase 3 ENABLAR-2 study is underway to further evaluate enobosarm monotherapy or in abemaciclib combination therapy in 2nd-line metastatic breast cancer population. Clinical trial information: NCT05065411. Research Sponsor: Veru Inc Citation Format: Kristine Rinn, Hannah Linden, Lee Schwartzberg, Gary Barnette, Domingo Rodriguez, Itay Shalev, Mitchell Steiner, Adam Brufsky, Joyce O'Shaughnessy. Design of Active Phase 3 ENABLAR-2 Study Evaluating Enobosarm +/- Abemaciclib in Patients with AR+ER+HER2- 2nd-Line Metastatic Breast Cancer Following Tumor Progression on an Estrogen Blocking Agent Plus Palbociclib or Ribociclib [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO4-27-06.

Abstract PO4-27-08: A Phase II Multi-Institutional Study of Concurrent Radiotherapy, Palbociclib, and HormoneTherapy for Treatment of Bone Metastasis in Breast Cancer Patients

Abstract Background: This Phase II study aimed to determine the efficacy and safety of administering palliative radiotherapy (RT) to bone metastases (mets) in patients (pts) receiving concurrent palbociclib and hormone therapy (HT) for hormone receptor positive, Her2/neu negative breast cancer. The primary endpoint was response rate 3 months after RT. Methods: Pts with painful bone mets or asymptomatic bone mets with risk for impending clinical event were treated with RT to 30 Gy in 10 fractions or 20 Gy in 5 fractions with concurrent palbociclib and HT. Change in maximum pain score on the Brief Pain Inventory was used to assess pain response 3 months post RT relative to baseline. Among pts with asymptomatic bone lesions, response was defined as prevention of a clinical event (e.g., bone fracture) without evidence of local tumor growth on surveillance imaging. Patient reported outcomes (PROs) of fatigue, depression, anxiety, and quality of life were collected. Blood-based biomarkers were examined to determine their relationship with response and PROs. Using a non-inferiority study design, a sample size of at least 33 pts was needed to achieve 80% power to detect a non-inferiority proportion of 60% using a one-sided binomial test and assuming a Type I error of 0.05. Results: Among 38 patients enrolled, 79% had painful bone mets. 35 pts completed baseline and 3-month post RT assessments. 61% and 37% of pts received aromatase inhibitors and fulvestrant, respectively, with palbociclib. Median age was 60 years (31-83) and 25% of pts were non-Hispanic Black. The majority (72%) of pts received 5 fraction RT and 69% received RT to one bone region. 29 patients (83%) were responders [95% CI: 66%-93%, p=.003]. Median progression free survival (PFS) was 30.4 months (1.3 - 44.0). Three-year PFS and overall survival were 45.6% and 67.2%, respectively. Grade 3 neutropenia developed in 4 (11%), 4 (11%), and 7 (20%) pts at end of RT, 1 month, and 3 months post RT, respectively. No pts developed Grade 4 neutropenia. One patient developed Grade 3 gastrointestinal toxicity during RT, another developed Grade 3 dyspnea 1 month post XRT, and another developed a bone fracture 6 months after RT. >While patient reported measures of fatigue, depression, and overall quality of life did not significantly change during or after RT relative to baseline, pain scores (i.e., BPI pain severity and interference, BM22 pain characteristics and pain site subscales, EORTC C15 pain) significantly decreased 3 months post XRT relative to baseline. Heightened inflammatory marker levels (e.g., TNFRII, IL1ra, CRP, TNF alpha) were significantly associated with worse symptoms of fatigue (MFI) and depression (HADS), increased pain interference (BPI), and lower overall quality of life (SF-36), controlling for age and time using mixed effect models. Patients with improved pain symptoms and lower pain scores had significantly lower inflammatory marker levels relative to baseline (e.g., interleukin-6). Conclusions: Our study demonstrated high rates of response to concurrent RT with palbociclib and HT with acceptable levels of toxicity. These results suggest that RT to bone mets effectively alleviates pain in patients taking palbociclib and pain response to treatment is associated with decreased inflammatory markers. RT may be given to pts receiving palbociclib and HT for breast cancer. Clinical Trial Identification: NCT03691493 Citation Format: Mylin Torres, Jolinta Lin, Sarah Friend, Canhua Xiao, Yichun Cao, Shannon Kahn, Karen Godette, Sheela Hanasoge, David Yu, Tony Eng, Matthew Cheney, Nancy Wiggers, Andrew Pippas, Keerthi Gogineni, Jane Meisel, David Schuster, Aditya Bardia, Andrew Miller, Jennifer Felger, Jeffrey Switchenko, Amelia Zelnak, Kevin Kalinsky, Manali Bhave. A Phase II Multi-Institutional Study of Concurrent Radiotherapy, Palbociclib, and HormoneTherapy for Treatment of Bone Metastasis in Breast Cancer Patients [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO4-27-08.

Abstract PO3-02-12: Dalpiciclib combination with letrozole as neoadjuvant therapy for HR-positive HER2-negative breast cancer: a single-arm, prospective exploratory clinical study

Abstract Background: CDK4/6 inhibitors effectively block tumor cells from progressing from the G1 phase to the S phase, thereby interrupting the cell cycle progression and inhibiting tumor cell proliferation. Dalpiciclib is a novel CDK4/6 inhibitor developed independently in China, which has been approved for use in combination with fulvestrant for the treatment of HR-positive/HER2-negative recurrent or metastatic breast cancer in patients who have experienced disease progression after prior endocrine therapy, or in combination with aromatase inhibitors as initial treatment for HR-positive/HER2-negative locally advanced or metastatic breast cancer patients. This study aims to explore the efficacy and safety of dalpiciclib in combination with letrozole as neoadjuvant therapy for HR-positive, HER2-negative breast cancer. Methods: This is a single-arm, open-label study that enrolled female breast cancer patients with early or locally advanced HR-positive, HER2-negative tumors and an ECOG performance status of 0 to 1. After enrollment, patients first received 4 cycles of dalpiciclib (150mg po qd, d1-21, q4w) in combination with letrozole as neoadjuvant therapy. Breast MRI was performed every 2 cycles, and treatment response was evaluated according to the RECIST 1.1 criteria. If patients achieved a confirmed complete response (CR) or partial response (PR) after 4 cycles, they would continue to receive an additional 4 cycles of dalpiciclib in combination with letrozole treatment. If the treatment response was stable disease (SD) or disease progression (PD), the investigator might modify other treatment regimens based on the individual circumstances of the subjects. The primary endpoint was residual cancer burden (RCB 0/I), and the secondary study endpoints were objective response rate (ORR), complete cell cycle arrest (CCCA, C1D15 Ki67≤2.7%) rate and safety. This study is registered at the Chinese Clinical Trial Registry Centre (registration No. ChiCTR2200057104). Results: From April 2022 to June 2023, a total of 38 patients were screened and enrolled in the study. All patients had ER ≥ 50%, and 84% (32/38) had Ki67 ≥ 88%. Among the 21 patients who completed the assessment after 4 cycles, the overall response rate (ORR) was 81% (17/21). Additionally, among the 22 patients who underwent C1D15 biopsy and Ki67 analysis, 55% (12/22) had C1D15 Ki67 ≤ 2.7%. After completing 8 cycles of neoadjuvant treatment with the combination of dalpiciclib and letrozole,12 patients underwent surgery. The postoperative RCB scores were as follows: 1 patient had RCB (0-I), and 11 patients had RCB (II-III). The most common adverse event was decreased neutrophil count (25/38 [66%]). Among the 38 patients, 16 (42%) experienced grade 3 or worse treatment-related adverse events. There were no occurrences of grade 4 or worse adverse events. Conclusions: The combination of dalpiciclib and letrozole has shown efficacy in downstaging and shrinking tumors in patients with early or locally advanced HR-positive/HER2-negative breast cancer. Patients who exhibit a positive response in the assessment after 4 cycles may consider it as a viable option for chemo-free neoadjuvant treatment. Citation Format: Jingruo Li, Yuanting Gu, Chuang Du, Jianhua Zhang, Yingying Zhang, Linfeng Zhang, Nan Wang, Lin Li, Fang Wang, Pengwei Lv, Hong Zong, Xinhong Pei, Bingjian Xue, Yan Wang, Dongcheng Gao. Dalpiciclib combination with letrozole as neoadjuvant therapy for HR-positive HER2-negative breast cancer: a single-arm, prospective exploratory clinical study [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO3-02-12.

Abstract PO2-27-03: Clinical Results of Subjects Remaining in the Phase 3 ARTEST Study Enobosarm Therapy in AR+ER+HER2- Metastatic Breast Cancer with 3 or Greater Prior Lines of Therapy

Abstract Background: Targeting the androgen receptor (AR) with an oral selective AR agonist, enobosarm, is a novel approach to overcome ER and CDK4/6 inhibitor resistance to suppress AR+ER+HER2- metastatic breast cancer (mBC). Preclinical studies in CDK4/6 inhibitor and estrogen blocking agent resistant PDX mBC models demonstrated that enobosarm alone suppressed tumor growth. In a small subgroup analysis of patients with ER+HER2- mBC who progressed on estrogen blocking agent and a CDK 4/6 inhibitor from the Phase 2 802 study, enobosarm treatment resulted in a best overall response rate of 30% (2 CRs and 1 PR) and a 6-month clinical benefit rate (CBR) of 50%. Methods: The clinical activity of enobosarm 9mg alone was evaluated compared to standard of care (SOC) in the Phase 3 ARTEST, open-label, randomized, multicenter study in AR+ER+HER2-mBC who have progressed on 2 or greater lines of prior therapies, including estrogen blocking agents and CDK4/6 inhibitors. The study was discontinued for administrative reasons not related to efficacy or safety. Results: At the time study was discontinued, 34 patients with confirmed AR positivity were randomized to either enobosarm (n=16) or SOC control (n=18). SOC control treatment group received an average of 2.6 (range 1-5) and enobosarm 9mg monotherapy an average of 2.9 (range 1-5) prior lines of treatment. On average, enobosarm or the SOC control was given in the 4th line treatment for AR+ER+HER2- metastatic breast cancer. In the evaluable population, two partial responses were observed in the enobosarm treatment arm versus no responses in the SOC control arm. In patients with ≤3 lines of prior endocrine therapy, the best objective response rate (ORR) was 18.8% for enobosarm and 0% for control. In patients with ≤3 lines of prior endocrine therapy with ≤1 prior treatment with CDK 4/6 inhibitor, best ORR was 33% in the enobosarm group versus no responses in the SOC control (Table 1). CBR on day 180 was 33.3% (4/12) in the enobosarm group vs 0% (0/11) in the control group. Enobosarm treatment was well tolerated without masculinizing adverse events and no increases in hematocrit changes. Conclusions: Activity of enobosarm in this heavily pretreated patient population is encouraging and supports further clinical investigation. The Phase 3 ENABLAR-2 study is underway to further evaluate enobosarm alone or in combination with abemaciclib for the second-line treatment of AR+ER+HER2- metastatic breast cancer in patients who have received a prior estrogen blocking agent and a CDK 4/6 inhibitor. Clinical trial information: NCT04869943. Research Sponsor: Veru Inc. Table 1. Responses in patients with enobosarm versus SOC treatment. Citation Format: Kristine Rinn, Elisa Krill Jackson, Gary Barnette, Domingo Rodriguez, Itay Shalev, Mitchell Steiner, Joyce O'Shaughnessy, Hope Rugo, Adam Brufsky. Clinical Results of Subjects Remaining in the Phase 3 ARTEST Study Enobosarm Therapy in AR+ER+HER2- Metastatic Breast Cancer with 3 or Greater Prior Lines of Therapy [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO2-27-03.