Positive HER2 Negative Breast Cancer Research Articles

Estrogen-Receptor Loss and ESR1 Mutation in Estrogen-Receptor-Positive Metastatic Breast Cancer and the Effect on Overall Survival.

In patients with metastatic estrogen-receptor (ER)-positive HER2-negative breast cancer, the loss of ER expression and the mutation of ESR1-the gene encoding the ER receptor-are mechanisms for resistance to endocrine therapy. We aimed to determine the frequency of these mechanisms and their interaction. Metastases were retrieved from our pathology files. ESR1 hotspot mutations resulting in p.(D538G), p.(Y537S), and p.(L536H) were determined by means of pyrosequencing. Clinical data were retrieved from electronic medical records. A total of 136 metastases were available for analysis. ER loss was found in 23 metastases (17%). ESR1 mutations were found in 18 metastases (13%), including p.(D538G) in 9, p.(Y537S) in 7, and p.(L536H) in 2. ESR1 mutation and ER loss were mutually exclusive (p = 0.042), and ESR1 mutation was associated with endocrine therapy (p = 0.002). ESR1 mutation was found in two primary breast cancers. ESR1 mutations are rare in primary breast cancer and develop in metastases during endocrine therapy. Furthermore, ER loss had a statistically significant negative effect on overall survival when compared to patients without ER loss, with a rate ratio of 3.21 (confidence interval 1.95-5.26). No such effect was observed for ESR1 mutations, with a rate ratio of 1.15 (confidence interval 0.67-1.95). We conclude that ER loss and ESR1 mutation together account for 30% of the resistance to endocrine therapy.

Use of Oncotype vs. Breast Cancer Index (BCI) for extended endocrine therapy decisions: A single center analysis in stage IA hormone receptor positive breast cancer.

e13083 Background: Extended Endocrine Therapy (EET) for hormone receptor positive HER-2 negative early-stage breast cancer reduces late recurrence risks but raises concerns about toxicity. Biomarker tests like the Breast Cancer Index (BCI) are vital for identifying patients who could benefit from continued ET, reassuring others against unnecessary extension. This study evaluates prognostic implications for both Oncotype Dx (Recurrence score, RS) and BCI amidst concerns about added testing costs in patients with early stage, estrogen receptor (ER) positive breast cancer. Methods: This is a single institution retrospective review of Stage IA ER positive HER-2 negative breast cancer patients who underwent both Oncotype Dx and BCI testing from January 2021 to December 2023. Pearson's correlation coefficient (r) was used to assess the linear relationship between the assays (p<0.05 for significance), analysis was performed with SAS software, version 9.4. Results: Fifty-eight patients with Stage IA ER positive HER-2 negative breast cancer who had both Oncotype and BCI results were identified (100% female; mean age 72.2 years [54-87]). After a median followed up of 72 months (63-75), no systemic or locoregional recurrences were reported. A low positive correlation between Oncotype and BCI was observed across the entire cohort (r=0.4058; p=0.0016). However, subgroup analysis showed no significant correlations: Oncotype <11 (n=17; r=0.2415; p=0.3504), Oncotype ≤18 (n=43; r=0.0914; p=0.5600), Oncotype <26 (n=51; r=0.2530; p=0.0733); Oncotype ≥26 (n=7; r=-0.5634; p=0.1878). Correlation was also not found in patients with Grade 1 tumor (n=16; r=0.3138; p=0.2365). Thirty-nine patients (67.24%) had their treatment recommendation changed based on BCI results. Side effects from ET affected 15 patients (25.86%) and included arthralgias (60%, n=9), hot flashes (26.67%, n=4), depression (13.33%, n=2), insomnia (6.67%, n=1), and others (53.3%, n=8). Twenty-two patients (37.93%) developed new osteopenia, and 6 (10.34%) new osteoporosis while on EET. Eight patients (13.79%) had ET interruption during their treatment course. Conclusions: Despite inclination towards cost-saving measures, Oncotype DX may be more useful to give prognosis in the early adjuvant period whereas BCI is more useful to evaluate late recurrence risk. Low or high Oncotype scores and tumor grade may not align with BCI findings. Considering the importance of managing toxicity against the risk of late recurrence, incorporating BCI testing can enhance EET recommendations, even for Stage I, node-negative, ER positive patients.

A phase II trial comparing dalpiciclib in combination with letrozole versus standard chemotherapy as neoadjuvant therapy in patients with high-risk HR- positive HER-2 negative breast cancer: DARLING-02.

TPS626 Background: Dalpiciclib is a CDK4/6 inhibitor that has shown promising efficacy and safety when in combination with endocrine in the treatment of advanced HR+ HER2- breast cancer. Building on preliminary findings from our previous study (Geng, 2023SABCS PO2-02-05), we aim to evaluate the efficacy and safety of dalpiciclib combined with letrozole versus standard chemotherapy as neoadjuvant treatment in patients with high-risk early breast cancer (EBC). Methods: This is a prospective, multicenter, randomized phase II non-inferiority trial. Main eligibility criteria include: female patients ≥18 years, ECOG performance status of 0-1, histologically confirmed invasive breast cancer, clinical stage T1c-T2, cN1–2 or T3-4, cN0-2, ER≥50%, HER2-negative, and Ki67 ≤ 20%. Participants are randomized 1:1 to receive either 24-week experimental intervention (oral dalpiciclib 150mg once daily for 3 weeks on, 1 week off and oral letrozole 2.5 mg/day) or 24-week standard intervention (intravenous epirubicin 100 mg/m² and intravenous cyclophosphamide 500 mg/m² on day 1 for three 3-week cycles, followed by intravenous docetaxel 100 mg/m2 on day 1 for three 3-week cycles). The primary endpoint is the objective response rate (ORR) assessed by RECIST v1.1. Secondary endpoints include patient-reported outcomes (EORTC QLQ-C30, EORTC QLQ-BR23), residual cancer burden 0–I rate, preoperative endocrine prognostic index score 0 rate, pathological complete response rate , 2-year invasive disease-free survival rate, and safety. Exploratory endpoints include biomarker analysis. The hypothesis is that the experimental group will not be inferior to control group. Assuming an ORR of 70% for both groups, a sample size of 65 patients per group is required to achieve 80% power to detect a non-inferiority margin of up to 20% at a two-sided significance level of 5%. A total of 130 patients are needed (65 per group). Considering a dropout rate of 10% per group, the total sample size is approximately 144 patients. The trial was registered at ClinicalTrials.gov (NCT06107673) and is actively recruiting. Clinical trial information: NCT06107673 .

Abstract PO2-15-01: EZH2 protein expression in early hormone receptor positive HER2 negative breast cancer with high recurrence score

Abstract Background: The 21 gene recurrence score assay (RS) is both prognostic and predictive of chemotherapy benefit in hormone receptor positive (HR+) HER2 negative (HER2-) breast cancer (BC). While patients (pts) with RS>26 benefit from chemoendocrine therapy, they remain with poorer outcomes than pts with lower RS. Overexpression of the enhancer of zeste homolog 2 oncoprotein (EZH2) is linked to poor prognosis in multiple cancers, and is associated with resistance to endocrine therapy in HR+/HER2- BC. We evaluated association between EZH2 expression and distant metastases in a single institution cohort of pts with HR+/HER2- BC and RS>26. Methods: Pts with ER+/HER2- BC and RS>26 who underwent surgery at our institution between 2011 and 2017 were identified from pathology database. All pts with available tumor specimens were included in analysis. Immunohistochemistry was performed to evaluate EZH2 protein expression within invasive tumor cells and quantified as follows: nuclear staining intensity was scored as 3 (strong), 2 (moderate), 1 (weak), and 0 (no stain). Percentage of positive nuclei at each intensity was multiplied, and all values were added to arrive at a final EZH2 score multiplied by 100, ranging from 0 (no nuclei staining) to 300 (strong nuclear staining in 100% of cells). The investigator scoring EZH2 staining was blinded as to pts clinical outcomes. EZH2 score was both evaluated as a continuous variable and dichotomized at a score of 140. Associations between EZH2 score and age at diagnosis, progesterone receptor (PR) status, tumor size, grade, node involvement, RS, and metastatic recurrence were determined by Kruskal-Wallis or Wilcoxon rank-sum tests for categorical variables and Spearman correlation coefficients for continuous variables. Results: 45 pts were included. Median (IQR) age was 60 (55, 69). 32 (71.1%) pts received chemotherapy. 37 (82.2%) pts received endocrine therapy. Tumor size was ≤2 cm in 26 pts (57.8%), and >2 cm but ≤5 cm in 19 pts (42.2%). 7 pts (15.6%) had involved axillary nodes. Median RS was 31 (28, 37). Median EZH2 score was 120 (90, 170). With median follow-up of 7.6 (5.7, 9.2) years, 4 pts (8.9%) developed distant metastatic disease. EZH2 score was significantly associated with development of metastatic disease, both when EZH2 was expressed as a continuous variable (p=0.040) and when dichotomized at 140 (p=0.015). EZH2 score was positively associated with RS (r = 0.37; p=0.013) and negatively associated with age at diagnosis (r = -0.44; p=0.002), but was not associated with clinicopathologic features such as tumor size, grade, node involvement, and PR status. Younger age was also associated with development of metastatic disease (p=0.023), whereas tumor size, grade, node involvement, PR status, RS, and receipt of chemotherapy were not. Conclusion: In this single institution cohort of pts with early HR+/HER2- BC and high RS, EZH2 protein expression and younger age were associated with development of distant metastases. This preliminary data suggests that determination of EZH2 expression levels may assist in risk stratification of pts with high RS. This should be investigated in a larger data set. Citation Format: Shuwen Lin, Yungtai Lo, Della Makower, Jinyu Lu, Susan Fineberg. EZH2 protein expression in early hormone receptor positive HER2 negative breast cancer with high recurrence score [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 PO2-15-01.

Abstract PO4-16-11: De-escalation of anthracyclines during adjuvant therapy based on Oncotype RS: A single institution experience in Mexico City

Abstract Introduction: In Mexico, hormone positive HER2 negative breast cancer is the most frequent subtype, accounting for 76.6% of cases. For patients undergoing local control management through surgery; adjuvant chemotherapy is usually followed depending on different risk factors. In order to avoid overtreatment, different genomic firms have been approved aiding in a more objective decision. One of these genomic firms is the Oncotype Recurrence score. The TAILORx and RxPONDER trials have provided guidance in determining which patients are candidates for chemotherapy depending on their menopausal status. However, it has not yet been determined whether patients requiring chemotherapy can receive an anthracycline-free regimen. In the Plan B clinical trial, a non-inferiority analysis was conducted on early-stage breast cancer patients who received anthracycline-based or non-anthracycline-based chemotherapy, with the non-anthracycline regimen being non-inferior, including patients with a RS > 25. We intend to reevaluate these findings in our Mexican population. Methods: We evaluated 217 patients with early stage hormone sensitive HER2 negative breast cancer who had an Oncotype Recurrence score (RS) result. This retrospective cohort study took place by analyzing electronic records from January 2011 to December 2017 with patients treated at the National Cancer Institute in Mexico City. We included patients 18 years of age or older, any sex with an Oncotype RS ≥ 16 in premenopausal patients or ≥ 26 in postmenopausal patients who received adjuvant chemotherapy with or without anthracyclines. Our primary endpoint was iDFS comparing TC vs AC-T. Overall survival was set as a secondary endpoint. Results: Of the 217 patients with an Oncotype recurrence score, only 46 patients received adjuvant chemotherapy of which 71.7% were premenopausal with a median age of 45 years. Stage II was the most common stage with 91.3% of the population, as well as ductal carcinoma with 82.6%. All patients had positive lymph nodes, 54.3% at least 1 lymph node. Most patients received AC-T adjuvant chemotherapy (60.9%), and only 39.1% received TC. Of the 46 patients analyzed, only 19.6% (9) had a recurrence upon follow-up (Table 1). Median time of follow up was 87.5 months. Difference in Disease free survival could not be established between patients receiving AC-T with 105 months (CI 95% 94.36-117.43 months) vs TC with 94.09 months (CI 95% 83.85-104.34 months, < p.918) (Figure 1). Overall survival did not have a statistical difference between both chemotherapy regimens, p< 0.649 (Figure 2A), when comparing Oncotype RS, overall survival was better in those with Oncotype OS < 26, p< 0.023 (Figure 2B). Discusion As described previously in the Plan B trial, TC was non inferior to the conventional adjuvant regimen of AC-T in Hormone positive HER2 negative early-stage breast cancer. Our results tend to show similar results when compared to the Plan B. An important aspect to our study was that 71.7% of our patients were premenopausal, where in the Plan B trial only 35% were premenopausal, considered a higher risk group of patients. Although a statical difference couldn´t be established due to our small sample size, in DFS or OS when comparing the chemotherapy regimen. Premenopausal patients with an Oncotype RS < 26 could receive an anthracycline free regimen, without impact in their overall survival. Larger prospective studies are necessary to assure this conclusion. Figure 1 DFS (TC vs AC-T) Figure 2 A and B Overall Survival Table 1 (Baseline characteristics) Citation Format: Carlos Arturo González Núñez, Paula Cabrera-Galeana, Juan Enrique Bargalló Rocha, Rafael Vazquez-Romo, Sergio Aguilar-Villanueva, Alexandra Garcilazo, Areli Velazquez-Martinez, Andrea Maliachi, Ruben Rodriguez, Esmeralda Romero-Bañuelos. De-escalation of anthracyclines during adjuvant therapy based on Oncotype RS: A single institution experience in Mexico City [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 PO4-16-11.

Abstract PO5-20-04: A Phase II Study of Ribociclib and Endocrine Treatment of Physician’s Choice for Locoregional Recurrent, Resected Hormone Receptor Positive HER2 Negative Breast Cancer (RaPhLRR Study)

Abstract Background Hormone receptor positive (HR+) breast cancer (BC) is the most common subtype of BC (70-80%). This subset tends to have good prognosis, therefore most patients with localized disease have excellent long-term survival, approaching 100% 5-year relative survival. However, 10% of patients experience loco-regional recurrence (LRR) within 5 year of final surgical management of the primary disease-well within the typical treatment window of adjuvant endocrine therapy. Few studies exists to guide the systemic treatment of patients who have suffered LRR of HR+ HER2 - BC. The randomized controlled CALOR trial demonstrated no benefit to systemic cytotoxic chemotherapy for this subgroup of patients and persistent high rate of subsequent recurrences (50% within 10 years on LRR event). There is no standard of care for managing this patient population. The combination of ribociclib and endocrine therapy (ET) (fulvestrant and aromatase inhibitors) is FDA approved for management of unresectable recurrences and metastatic HR+HER- BC (MONALEESA trials). CDK4/6 inhibitors have been investigated in early BC setting too, several trials showing positive results (monarchE, NATALEE). Data is needed to investigate their use in patients with LRR. Trial design This is a multicenter, single arm phase II study to evaluate efficacy and safety of ribociclib and ET in patients with LRR of HR+HER2- BC. Treatment includes ribociclib for 36 months, 600 mg daily for 21 days, 28-day cycle plus physician’s choice ET for 60 months (fulvestrant or AIs). Ribociclib dose was chosen based on approved dose in metastatic BC. Eligibility Criteria Patients ≥ 18 of age, with LRR of BC (ipsilateral breast, axilla, regional lymph nodes, chest wall), histologically confirmed estrogen receptor positive and/or progesterone receptor positive, HER 2 negative. Patients must have adequate local treatment for LRR (surgery and/or radiation) with negative microscopic margins, no evidence of distant metastatic disease. Prior treatment with neo-adjuvant and adjuvant chemotherapy and ET is allowed, no prior CDK 4/6 inhibitor in the last 12 months. Pre and post-menopausal women are allowed. Patient must enroll within 6 months of the last local therapy. Specific aims Primary objective: to estimate subsequent recurrence-free survival (RFS) at 3 years for ribociclib when administered with ET in patients with HR + HER2- BC with adequately resected local recurrence. Secondary objectives: to estimate distant metastasis-free survival and overall survival, to evaluate safety and tolerability, to identify predictors of LRR. Correlative analysis will explore prognostic and predictive biomarkers of treatment with ribociclib and ET and potential molecular mechanisms of resistance to treatment. Statistical Methods From previous published data (J Clin Oncol. 2018 Apr 10;36(11):1073-1079), we assume that patients receiving standard of-care management following recurrence would have a recurrence free survival (RFS) rate of 80% at 3 years and that treatment with ribociclib + ET will increase it by 7%. We wish to have at least 80% power at that significance level of 0.0487 to correctly detect that improvement in RFS rate at 3 years from 80 to 87%. Because only an improvement in RFS rate is of clinical interest, we have a directional hypothesis, and have used a 1-sided alpha. Using a one-sample survival study design, with assumed accrual duration of 3-years and additional follow-up time of 3 years, the minimum sample size requirement is N=180 patients. Target accrual The minimum sample size requirement is N=180 patients. A bigger sample size of N=200 patients will achieve a power of at least 84%. Current accrual is 6/200. This study will be open at up to 35 sites. Contact information The study is being administered through the HCRN, it can be identified as BRE20-468, NCT05467891, ocdanciu@uic.edu Citation Format: Oana Danciu, Nancy Chan, Kari Wisinski, Trish Millard, Kathleen Kemmer, Sneha Phadke, Zhengjia Chen, Ana Cuesta Fernandez, Melanie Clark, Alison Conlin, Coral Omene, Sima Ehsani, Stephanie Dublis, Vijayakrishna K. Gadi. A Phase II Study of Ribociclib and Endocrine Treatment of Physician’s Choice for Locoregional Recurrent, Resected Hormone Receptor Positive HER2 Negative Breast Cancer (RaPhLRR 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 PO5-20-04.

Abstract PO3-05-05: The effect of histological breast cancer subtype on progression free survival in patients with CDK4/6 inhibitors

Abstract Background: Multiple trials have proven that adding CDK4/6 inhibitors to endocrine treatment increases progression free (PFS) and overall survival (OS) of patients with metastatic estrogen receptor (ER)-positive HER2 negative breast cancer. However, only limited evidence is available of treatment efficacy of CDK4/6 inhibitors for invasive lobular carcinoma (ILC). This retrospective study aims to compare treatment duration of the three FDA/EMA approved CDK4/6 inhibitors in patients with no special type (NST) breast cancer versus patients with ILC. Methods: All patients with metastatic ER-positive HER2-negative breast cancer who were treated with a CDK4/6 inhibitor (1st, 2nd; 3rd line) in University Hospitals Leuven between December 2014 and February 2023, were included. A comparison of PFS and OS was made between patients with NST and ILC by use of the Kaplan Meier method. Other histological subtypes as well as mixed subtypes were excluded. Uni- and multivariable cox regression models were performed to quantify the association of histological subtype with PFS and OS. Results: A total of 418 patients were included of which 119 (28.5%) patients with ILC (median age at primary diagnosis 59 years, range 36 – 89 years) and 299 (71.5%) patients with NST (median age at primary diagnosis 55 years, range 23 – 90 years). Median follow-up was 26.8 months (range 1.1 – 88.1 months). Median PFS was 15.2 months (range 1.0 – 74.6 months) and 14.7 months (range 1.0 – 89.3 months) for patients with ILC and NST respectively. The OS rate after 60 months follow up was 39.2 % (CI 26.8 – 51.4) for ILC and 40.1% (CI 32.2 – 47.8) for NST. As shown in table 1, clear differences were observed in PFS rates after 12, 24 and 60 months between patients with NST that received CDK4/6 inhibitors in first line versus second or third line. These differences were less apparent for patients with ILC. For both NST and ILC, endocrine resistance at start of CDK4/6 inhibition impacted PFS rates negatively (table 2). In multivariable analyses, histological subtype was not predictive for CDK4/6 inhibition outcome (PFS: hazard ratio (HR) 0.996, CI 0.728 – 1.364, p-value 0.981; OS: HR 0.872, CI 0.602 – 1.263, p-value 0.468). Endocrine sensitivity vs. resistance at the time CDK4/6 inhibitor was started, was proven to be predictive for both PFS (HR 0.478, CI 0.337 – 0.678, p-value < 0.001) and OS (HR 0.528, CI 0.347 – 0.804, p-value 0.003). Conclusion: In our center, the histological subtype of breast cancer did not seem to impact PFS and OS significantly after treatment with CDK4/6 inhibition. Patients with NST seemed to have an increased benefit in PFS from treatment with CDK4/6 inhibition in first line as compared to later lines. While for patients with ILC, no difference between treatment lines were observed. Therefore, clinicians might be able to safely postpone CDK4/6 inhibitors to second- or third-line treatment in patients with metastatic ILC. Table 1: PFS rates by histological subtype and line of CDK4/6 treatment Table 2: PFS rates by histological subtype and endocrine sensitivity at start of CDK4/6 inhibition Citation Format: Cedric Bauters, Karen Van Baelen, Hans Wildiers, Giuseppe Floris, Sileny Han, Patrick Berteloot, Thaïs Baert, Ann Smeets, Ines Nevelsteen, Yannick Van Herck, Anne Deblander, Chantal Remmerie, Lieke Dullens, Maxime Van Houdt, Annouschka Laenen, Christine Desmedt, Patrick Neven. The effect of histological breast cancer subtype on progression free survival in patients with CDK4/6 inhibitors [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 PO3-05-05.

Abstract PO4-15-03: Quantitative Measurement of TROP2 via Chromogenic Immunohistochemistry in Breast Cancer

Abstract Sacituzumab govitecan (SG) is an antibody-drug conjugate that targets human trophoblast cell-surface antigen 2 (TROP2), which is expressed in over 90% of breast cancer cases (Zaman et al, 2019). By delivering the cytotoxic SN-38 (topoisomerase I inhibitor) to TROP2 expressing breast cancer cells, SG showed promising antitumor activities in clinical trials and is now an approved treatment for triple-negative breast cancer (TNBC) and hormone receptor (HR)-positive HER2-negative breast cancer in the metastatic setting. Despite the prevalent expression of TROP2 in breast cancer, the objective response rates reported from clinical trials were about 30%, indicating the need for a diagnostic test that can identify which patients are likely to benefit from therapy. Although the drug is approved without a companion diagnostic assay, recent data from the TROPiCS-02 trial has shown that TROP2-low (H-score < 100) showed a non-significant hazard ratio for benefit from SG. In the same study, patients treated with SG with H-score >100 showed a significant hazard ratio for benefit compared to physician’s choice (Tolaney et al, ASCO 2023). This suggests that TROP2 expression level is associated with SG response and that a threshold for TROP2 expression level may aid patient selection. Although over 90% of breast cancer patients were considered TROP2-positive by IHC, the expression level of TROP2 was never quantitatively assessed in large breast cancer cohorts. Here we describe a quantitative chromogenic immunohistochemistry (IHC) assay with a cell line standard. Mass spectrometry was used to measure TROP2 peptide concentrations in the six standard cell lines, and the correlation between the mass spectrometry and IHC data for each cell line was then used to convert chromogenic signals to concentrations of TROP2 protein (fmol/mm2). The antibody used in this assay was rigorously validated, and the antibody concentration was optimized for the best signal-to-noise ratio. The optical density (OD) of chromogenic staining was measured using QuPath 0.4.3 (Qymia extension) by identifying the tumor area via object classifiers and manual editing and then calculating the area-normalized sum of OD. Collectively, this assay can measure up to 29.1 fmol/mm2 of TROP2. By applying this assay to two serial retrospective primary breast cancer cohorts from Yale University, we quantitatively measured TROP2 expression levels in 332 clinical cases. Not surprisingly, over 90% of cases showed some chromogenic signal, with a median TROP2 concentration of 2.1 fmol/mm2 and a maximum of 10.5 fmol/mm2. TROP2 expression levels showed no significant association with clinicopathologic characteristics including race, stage, BRCA mutation status, molecular subtype, HER2 IHC levels, and outcome. Further work is underway to optimize the assay toward the goal of determination of whether there is a quantitatively definable threshold for TROP2 expression below which patients are unlikely to benefit from SG or other TROP2-targeted therapies. Citation Format: Mengni He, Matthew Liu, Thazin Aung, Sneha Burela, Katherine Bates, Charles Robbins, David Rimm. Quantitative Measurement of TROP2 via Chromogenic Immunohistochemistry in 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 PO4-15-03.

Impact of HER2 low expression in the Oncotype DX RS in patients with operable hormone receptor positive early stage breast cancer.

575 Background: Two thirds of breast carcinomas are human epidermal growth factor receptor 2 (HER2) low. To date, it is still unclear whether hormone receptor (HR) positive HER2 low tumors represent a distinct biological subtype. HER2 low status is not considered an independent predictive factor for benefit from adjuvant chemotherapy in HR positive early breast cancer. We aim to investigate the impact of HER2 low expression on the established predictive biomarker Oncotype DX RS in a cohort of patients with HR positive HER2 negative early breast cancer. Methods: Retrospective study of patients with stage I-III HR positive HER2 negative breast cancer treated with upfront surgery between 2019-2022 at the Weill Cornell Breast Center and for whom Oncotype DX RS test was available. Patients were grouped to HER2-0 (immunohistochemistry (IHC) score of 0) or HER2 low (IHC score of 1+ or, 2+ with non-amplified in situ hybridization) expression. Clinicopathological characteristics and Oncotype DX RS were compared across the different categories of HER2 expression. Results: Of 509 patients included, 37% and 63% were grouped as HER2-0 and HER2 low, respectively. Median age at diagnosis was 61 years [IQR 50-69]. Sixty-eight percent of patients were postmenopausal. Stage I, II and III corresponded to 76%, 23% and 1% of patients, respectively. Seven percent of patients had nodal involvement. Ductal carcinoma was the most common histological type (75%) followed by lobular carcinoma (17%). Most tumors had low-intermediate histological grade (81%) with a median Ki-67 of 10% [IQR 5-15]. No significant difference was observed in clinicopathological characteristics between the HER2-0 and HER2 low groups. The overall median Oncotype DX RS was 16 [IQR 11-21]. The median Oncotype DX RS based on a HER2 expression of 0, 1+ and 2+ was 15, 17 and 17, respectively. There was no statistically significant difference between the Oncotype DX RS score and HER2 expression, when comparing HER2-0 to HER2 low (p = 0.578), HER2-0 to HER2-1+ (p = 0.775) and HER2-0 to HER2-2+ (p = 0.157). In the pre-menopausal and lobular carcinoma subgroups, the median Oncotype DX RS was 15 [IQR 9-21] and 17 [IQR 12-22], respectively; and there was no statistically significant difference between the Oncotype DX RS score and HER2 expression (p > 0.05). Post-surgery, 87%, 66% and 13% of patients received endocrine therapy, chemotherapy and radiation therapy, respectively. Median follow up time was 16 months [IQR 8-34]. Disease recurrence was documented in 9 (2%) patients. Conclusions: In this study, we found no differences in the Oncotype DX RS and the prognostic pathological features between the HER2-0 and HER2 low groups which is in line with previous retrospective studies. Survival analysis was limited by the median follow up. Further studies on the understanding of the biology of HER2-low and its clinical implications in early breast cancer are needed.

Detection of circulating tumor DNA following neoadjuvant chemotherapy and surgery to anticipate early relapse in ER positive and HER2 negative breast cancer: Analysis from the PENELOPE-B trial.

502 Background: The PENELOPE-B phase III trial investigated the addition of one year of palbociclib to endocrine therapy (ET), in patients with hormone receptor positive HER2 negative breast cancer with residual invasive disease after neoadjuvant chemotherapy. Prior research has demonstrated that detection of circulating tumor DNA (ctDNA) in the adjuvant setting is associated with a high risk of disease relapse. We assessed the potential of ctDNA analysis to predict future clinical relapse for patients enrolled in the PENELOPE-B trial. Methods: Patients who were endocrine naïve at the time of study entry were selected for ctDNA analysis. Plasma samples were collected at baseline (after completion of neoadjuvant chemotherapy and surgery), prior to cycle 7 (approximately 6 months into ET +- palbociclib), end of treatment (EOT), and progressive disease. A tumor sample was subjected to exome sequencing, and up to 50 tumor somatic mutations were tracked in plasma using error-corrected sequencing combined with a proprietary algorithm for ctDNA detection (RaDaR assay). Detection of ctDNA was associated with invasive disease-free survival (iDFS) and distant metastasis-free survival using Cox proportional hazard models. Results: Of 1250 patients enrolled in PENELOPE-B, 129 were endocrine naïve at trial entry, and 78 had a baseline ctDNA sample analyzed. The ctDNA analysis group was representative of the overall endocrine naïve group, with median follow-up of 42.9 months. Seven patients had baseline ctDNA detected, with detection strongly associated with iDFS (HR 8.8, 95% CI 3.3-23.4, p < 0.0001). Detection of ctDNA at cycle 7 (4 patients) was also strongly associated with iDFS (HR 25.5, 95% CI 6.5-99.6, p < 0.0001). Of the 7 patients with baseline ctDNA detection, 2 had undetectable ctDNA at cycle 7 and remained progression free at 30 months, although one later relapsed; the 3 patients with detectable ctDNA at cycle 7 all relapsed within 25 months. Of the 12 patients with a distant relapse within 24 months, only 4 had ctDNA detected at baseline and 3 first at cycle 7/EOT. Of the 8 patients with distant relapse after 24 months, 2 had ctDNA detected at baseline and none first at cycle 7/EOT. Conclusions: Detection of ctDNA following neoadjuvant chemotherapy, and surgery, is associated with a very high risk of early relapse suggesting limited efficacy of adjuvant ET. Clinical imaging and studies of experimental therapy are warranted in this patient population. Testing ctDNA after recent neoadjuvant chemotherapy in luminal-A like breast cancer has relatively low ‘sensitivity’ for predicting future relapse, in particular for later relapses, in part suggesting that response to neoadjuvant chemotherapy may reduce ctDNA detection. Clinical trial information: NCT01864746 .

Abstract P5-09-05: A phase II, single-arm study of histone deacetylases inhibitor Tucidinostat and Exemestane as neoadjuvant therapy in patients with hormone receptor positive HER2 negative breast cancer (NeoTEE trial)

Abstract Background: Tucidinostat (formerly known as chidamide) plus exemestane is approved for postmenopausal patients with advanced, hormone receptor-positive breast cancer. We evaluated the efficacy and safety of tucidinostat plus exemestane as the neoadjuvant strategy in hormone receptor-positive early breast cancer patients. Methods: NeoTEE is an open-label, single-center, phase II study. Patients with HR-positive, HER2-negative and stage II/III breast cancer were enrolled at the First Affiliated Hospital of Sun Yat-sen University. Eligible patients received 25 mg oral exemestane once daily for 2 weeks followed by 30 mg oral tucidinostat twice weekly in combination with 25mg oral exemestane once daily for 24 weeks. GnRHa was used for premenopausal patients. Endpoints assessed here included objective response rate (ORR), complete cell cycle arrest (CCCA, Ki-67≤2.7%) at surgery, disease control rate (DCR), pathological complete remission (pCR) and safety. Results: Between July 2020 and July 2022, 26 patients were enrolled, of whom 24 were evaluable for response per RECIST 1.1 criteria. Partial response (PR) was observed in 18 patients, with an ORR of 75% (18/24). The DCR was 100%. Of the 14 patients with surgery, one patient achieved pCR and 8 patients were exempt from postoperative adjuvant chemotherapy. CCCA at surgery was 64.3% (9/14). The follow-up remains ongoing and updated results will be presented thereafter. Most adverse events (AEs) were grade 1 or 2. Grade 3 AEs occurred in 8 of 26 patients, the most common were neutropenia 19.2%, leukopenia 7.7%, anemia 3.8%, ALT increased 3.8%, pneumonitis 3.8%. Only 1 patient experienced grade 4 neutropenia. Grade 3/4 neutropenia recovered after dose reduction or discontinuation of tucidinostat. No patient received G-CSF. Conclusions: Tucidinostat combined with exemestane was well tolerated and demonstrated meaningful responses in neoadjuvant setting for women with early HR+/HER2- breast cancer. Further investigation is warranted. Clinical trial information: NCT04465097. Citation Format: zhen shan, nan shao, xiaoling zhang, huijuan shi, yanling zheng, jia luo, tiantian zhen, ruping chen, Ying Lin. A phase II, single-arm study of histone deacetylases inhibitor Tucidinostat and Exemestane as neoadjuvant therapy in patients with hormone receptor positive HER2 negative breast cancer (NeoTEE 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 P5-09-05.

Abstract OT1-01-01: A randomised phase II trial of palbociclib and fulvestrant vs standard endocrine therapy in patients with ER positive HER2 negative breast cancer and ctDNA detected molecular relapse during adjuvant endocrine therapy (TRAK-ER)

Abstract Background: Most patients with early stage oestrogen receptor positive (ER+) and HER2 negative breast cancer will be cured of their cancer. However, up to 20% of patients may experience disease recurrence in the first 10 years. Molecular relapse of ER+ breast cancer can be detected with circulating tumour DNA (ctDNA) before clinical relapse occurs. Palbociclib, a CDK4/6 inhibitor, plus fulvestrant, a selective oestrogen receptor degrader, is a standard first line therapy for patients with ER+ breast cancer who have relapsed on standard endocrine therapy. We designed TRAK-ER to establish a surveillance system for ctDNA detection and then to assess whether treating patients, who have ctDNA detected molecular relapse, with palbociclib and fulvestrant may defer or prevent relapse. Design: TRAK-ER is a phase 2 multi-centre, randomised, open-label parallel superiority trial in patients with ER+ early breast cancer, recruiting at centres in the UK and France. In the surveillance phase patients will be monitored for molecular recurrence with ctDNA testing. To be eligible for the surveillance phase patients must be aged 18 or over, have ER+ (≥10% or Allred score 6/8 or greater) and HER2 negative breast cancer and have completed their primary surgery, chemotherapy and radiotherapy. Standard endocrine therapy (GnRH analogues, aromatase inhibitors and tamoxifen) must have been received for a minimum of 6 months and a maximum of 7 years and be planned to continue for at least another 3 years. Inclusion criteria in patients who did not receive neoadjuvant chemotherapy are at least one of: (a) four or more involved axillary or positive supraclavicular lymph node; (b) tumour size >5cm; (c) one to three involved axillary lymph nodes together with at least one of: tumour size >3cm, grade 3 or a high genomic risk score. Patients who received neoadjuvant chemotherapy require at least one lymph node positive or a tumour size >3cm after chemotherapy. Invitae Personalized Cancer Monitoring (PCM TM) will be used for ctDNA analysis, a pan-cancer, tumour-informed liquid biopsy test that uses next-generation sequencing to detect minimal or molecular residual disease (MRD) in solid tumours. ctDNA analysis will be every 3 months for up to 3 years. Detection of ctDNA will trigger staging imaging. If no overt metastatic disease is identified, patients will be able to enter the treatment phase of the study, and be 1:1 randomised using minimisation to either remain on standard endocrine therapy or switch to palbociclib plus fulvestrant. Those who are allocated to remain on endocrine therapy are allowed to continue on the same therapy or change standard endocrine therapy. Duration of palbociclib and fulvestrant will be 2 years, or until relapse. Up to 1300 patients will enrol for tissue screening to allow 1100 patients to enter into ctDNA surveillance. 132 patients will enter the treatment part of the study. The primary endpoint of the surveillance phase is ctDNA detection rate. The primary endpoint of the treatment phase is relapse free survival (RFS). RFS will be calculated in the intention to treat population using Kaplan Meier methods from the date of randomisation to the date of recurrence or death from any cause. Secondary endpoints include relapse free interval, invasive disease free survival, distant recurrence free survival, overall survival and ctDNA clearance. (NCT04985266) Citation Format: Nicholas Turner, Edward R. Phillips, Catey Bunce, Marie Robert, Caroline Bailleux, Isaac Garcia-Murillas, Komel Khabra, Iain Macpherson, Ciara S. O’Brien, Alicia F. Okines, Carlo Palmieri, Peter Schmid, Claire Swift, Sabrina Yara, Simon Connolly, Jérôme Lemonnier, Dymphna Lee, Fabrice Andre. A randomised phase II trial of palbociclib and fulvestrant vs standard endocrine therapy in patients with ER positive HER2 negative breast cancer and ctDNA detected molecular relapse during adjuvant endocrine therapy (TRAK-ER) [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 OT1-01-01.

Abstract P2-03-06: Real world treatment of node negative low and intermediate recurrence score breast cancer

Abstract Introduction: Patients younger than 50 years old with node negative hormone receptor (HR) positive her2 negative breast cancer and oncotype Dx recurrence scores (RS) under 16 do not benefit from adjuvant chemotherapy. Those with a RS between 16-25 may have a marginal benefit from the addition of adjuvant chemotherapy, however a similar benefit may be achieved with adjuvant ovarian function suppression (OFS). The aim of this study is to describe real world treatment patterns and outcomes of premenopausal node negative patients with low and intermediate RS, with an emphasis on adjuvant OFS, endocrine therapy (ET), and menopausal status during adjuvant treatment. Methods: We retrospectively reviewed the records of all node negative patients under 50 years old who were sent for oncotype testing between 2008 and 2018. One hundred and sixty-five patients with low or intermediate RS were included in our analysis. Continuous variables were described using medians and interquartile range (IQR). Categorical variables were described as frequencies and percentages. Differences between categorical variables were analyzed with the chi squared test and survival was analyzed using the Kaplan-Meier method. The cox proportional hazards model was used to test the effect of multiple factors on survival. Breast cancer specific survival (bcss) was defined as the time to first breast cancer recurrence (local recurrence, second breast cancer, distant recurrence) and distant disease-free survival (ddfs) was defined as the time to any distant recurrence. Results: The median age was 44 (41-47) and median RS was 17 (14-20). Median follow-up time was 82 (61-108) months. One hundred and three (62.4%) patients had low clinical risk as defined in TailorX and 136 (82.4%) had intermediate RS. Fourteen (8.5%) patients with nodal micrometastases were also included. Only 5 (3%) patients received adjuvant chemotherapy and 74 (44.8%) received adjuvant OFS. Of the 91 (55%) of patients who did not received OFS, 21 (23%) went into menopause or underwent subsequent oopherectomy while on adjuvant ET. One hundred and three (62.4%) patients received adjuvant tamoxifen alone, 16 (9.7%) received an aromatase inhibitor alone, and 40 (24.2%) underwent an endocrine switch with all but 1 beginning treatment with tamoxifen. There were no significant differences in clinical risk or RS risk group between patients that received and did not receive OFS. There were 22 (13.3%) bcss recurrences. Twelve (7.2%) patients had a local recurrence, 5 (3%) patients had second breast cancers, and 5 (3%) had a distant recurrence as their first recurrence. Overall, only 6 (3.6%) patients had a distant recurrence. Both OFS and ET type were not significantly associated with bcss or ddfs. On univariate analysis menopause during ET was significantly associated with improved bcss (HR= 0.2, 95% CI 0.05-0.85), however on multivariate analysis it was no longer significant. Conclusion: With only 6 (3.6%) distant recurrences over a median follow-up of over 6.5 years node negative premenopausal women with low or intermediate RS treated in our institution show an excellent prognosis regardless of treatment type. Our results support the evidence that most of these patients do not need chemotherapy and suggests that most patients do not require OFS as well. Additional data examining the relationship between gene expression profiles and OFS benefit are needed to help guide OFS treatment in premenopausal patients who do not require chemotherapy. Citation Format: Opher Globus, Keren Levanon, Einav Nili-Gal Yam. Real world treatment of node negative low and intermediate recurrence score 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 P2-03-06.

Abstract P5-09-01: Neoadjuvant hormonal therapy plus palbociclib versus hormonal therapy plus placebo in women with operable, hormone sensitive and HER2-negative primary breast cancer

Abstract Background: Early biologic response to endocrine therapy, such as changes in Ki67 labeling index (LI), has been suggested to predict long-term outcomes in hormone sensitive breast cancer. The addition of a CDK4/6 inhibitor to endocrine therapy has been shown to augment biological response in breast cancer. Pre-operative Endocrine Prognostic Index (PEPI) scores, generated based on post-treatment Ki67 LI, have been shown to predict patient outcomes. EndoPredict® is a multigene assay that predicts the risk of distant recurrence in patients with operable estrogen receptor (ER)-positive HER2-negative breast cancer. This study was conducted to evaluate the efficacy of the neoadjuvant endocrine therapy plus palbociclib versus neoadjuvant endocrine therapy plus placebo. Patients and Methods: This is a phase III randomized, double-blind study of neoadjuvant hormonal therapy plus palbociclib versus neoadjuvant hormonal therapy plus placebo in untreated pre/peri- and post-menopausal women with operable, hormone receptor-positive (ER and/or progesterone receptor), HER2-negative breast cancer. The other major inclusion criteria included tumor size ≥ 15mm, T1c-3N0-1, Ki67 LI ≥14% by central assessment, and no previous history of radiotherapy or systemic therapy for breast cancer. Patients were randomly assigned 1:1 to receive 16 weeks of hormonal therapy plus palbociclib or hormonal therapy plus placebo. Hormonal therapy consisted of letrozole for post-menopausal patients and tamoxifen plus LH-RH agonist for pre/peri-menopausal patients. The co-primary endpoints included PEPI score and EPclin Risk Score, a score combining EndoPredict® molecular score with clinical factors. These scores were sequentially analyzed on a modified intent-to-treat basis according to the gatekeeping procedure: if statistical significance was detected on the PEPI score, the statistical significance of EPclin Risk Score would be assessed. The sample size was 100 patients in each arm, which was calculated with < 5% type I error rate (two sided) and 80% power. Results: Between 16 July 2019 – 7 July 2021, 141 eligible patients were randomized from 25 participating institutes in Japan, Korea, Taiwan, Hong Kong and Australia. One hundred twenty-six patients completed the treatment duration and surgical samples were collected to evaluate endpoints. All randomized patients were evaluable for safety assessment. Randomization was well-balanced in terms of age, menopausal status and cancer stage. The proportion of patients who had a low, moderate, or high PEPI score was 15.2%, 50.0% and 34.8% in the hormonal therapy plus palbociclib arm and 13.3%, 55.0% and 31.7% in the hormonal therapy plus placebo arm, respectively. There was no statistically significant difference in PEPI score between two arms (one-sided p-value=0.563). The proportion of patients who had a high risk EPclin Risk Score seemed lower in the palbociclib arm than in the placebo arm (62.1% vs 68.3%) although hypothesis testing was not performed on EPclin Risk Score because statistical significance was not detected on the PEPI score. No new safety signals were found in the study. Permanent discontinuation from the study in association with adverse events was reported for 7 (9.7%) patients in the hormonal therapy plus palbociclib arm and for 0 patients in the hormonal therapy plus placebo arm. Conclusions: The addition of palbociclib to neoadjuvant hormonal therapy did not improve efficacy measured by PEPI score. In palbociclib arm, the rate of patients who had a high risk EPclin Risk Score after treatment was lower than in placebo arm. Translational researches are ongoing to analyze molecular changes by treatments. The role of chemotherapy after neoadjuvant therapy is under investigation. Clinical trial identification: NCT03969121 Funding: Pfizer Inc. Citation Format: Takayuki Ueno, Louis W.C. Chow, Wonshik Han, Chiun Sheng Huang, G Bruce Mann, Satoshi Morita, Hironori Haga, Elham Fakhrejahani, Takayuki Kobayashi, Kenichi Inoue, Mariko Tokiwa, Hirofumi Suwa, Tomoyuki Aruga, Sachiko Minamiguchi, Yosuke Yamada, Yuko Tanabe, Masahiro Takada, Toshinari Yamashita, Hiroji Iwata, Chi-Feng Chung, Sachiko Takahara, Eriko Tokunaga, Shigeru Imoto, Eun Sook Lee, Yasuaki Sagara, Jee Hyun Kim, Richard H DeBoer, Hyun-Ah Kim, Hung Wen Lai, Ming-Feng Hou, Michelle White, Yoshiko Umeyama. Neoadjuvant hormonal therapy plus palbociclib versus hormonal therapy plus placebo in women with operable, hormone sensitive and HER2-negative primary 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 P5-09-01.

Abstract P5-12-03: Intratumor heterogeneity and intrinsic immune activation are associated with response to chemotherapy in BRCA-related breast cancers

Abstract Background Breast cancers in women with a germline BRCA1/2 mutation (gBRCAm) have homologous recombination deficiency (HRD) and are sensitive to therapies causing double-strand DNA breaks. In TBCRC 031 (INFORM), both neoadjuvant cisplatin and doxorubicin/cyclophosphamide (“AC”) in gBRCAm carriers resulted in a complete pathologic response in 18% and 26% respectively in patients with newly diagnosed HER2–negative breast cancer. Herein, we describe molecular features from tumor whole exome (WES) and transcriptome sequencing (RNAseq) associated with response. Methods TBCRC 031 (the INFORM Trial - NCT01670500) was a randomized phase II neoadjuvant trial comparing the efficacy of cisplatin versus AC in gBRCAm carriers with stage I-III HER2–negative breast cancer. Of 118 patients enrolled, 92 patients provided fresh frozen research biopsies, collected prior to chemotherapy initiation, which were subjected to WES and RNAseq. Variants were called using GATK best practices and intratumoral heterogeneity was inferred from mutations and variant allele frequencies using Mutant Allele Tumor Heterogeneity (MATH) scores. Mutational Signature 3 (Sig3) and Genomic Instability Score (GIS) were calculated with SigMA and scarHRD, respectively. RNAseq data were utilized to perform differential gene expression and functional analyses, while cellular deconvolution was performed with CIBERSORTx trained against breast cancer single cell data. Patients were grouped according to their residual cancer burden (RCB) as responders (RCB-0 or 1), or non-responders (RCB-2 or 3). P-values ≤ 0.05 were considered statistically significant and when appropriate, adjustment for multiple testing was performed using a false discovery rate ≤ 5%. Results Of the 92 patients with gBRCAm, 59 (64%) had triple-negative and 33 (36%) were hormone-receptor positive HER2-negative breast cancer, 40 (43%) were classified as responders and 52 (57%) as non-responders. WES analysis revealed that indices of HRD were high (Sig3 exposure predominant and GIS ≥ 42) across most samples irrespective of receptor status and not significantly different among responders and non-responders. In contrast, responders exhibited lower levels of intratumor heterogeneity than non-responders (median MATH 42.9 vs. 33.5, p = 0.01). 223 genes were differentially expressed between responders and non-responders following control for tumor hormone receptor status, BRCA1/2 mutation, and menopausal status. Pathways identified as significantly enriched in upregulated genes were indicative of intrinsic immune activation in responders (e.g., T-cell activation, immune response-signaling, and regulation of leukocyte activation). Cellular deconvolution of the tumor microenvironment confirmed that responders presented a higher proportion of T-cells (p = 0.025) and myeloid cells (p = 0.003) in the tumor samples, while perivascular-like cells were enriched in non-responders (p = 0.034). Conclusion In this analysis of the largest cohort of treatment-naïve gBRCAm breast cancer to date, we found that response to cytotoxic chemotherapy is associated with a transcriptional program of intrinsic immune activation and an increased population of intratumoral T-cells and myeloid cells. Lower levels of intratumor heterogeneity and higher immune activation were associated with response to chemotherapy gBRCAm carriers while HRD scores were not. Citation Format: Felipe Batalini, Doga C. Gulhan, Xanthi Lida Katopodi, Nikolas Kalavros, Antuan Tran, Dimitra Karagkouni, Emily Stern-Gatof, Stuart Schnitt, Judy E. Garber, Gerburg M. Wulf, Peter J. Park, Ioannis Vlachos, Nadine Tung. Intratumor heterogeneity and intrinsic immune activation are associated with response to chemotherapy in BRCA-related breast cancers [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 P5-12-03.

149P Clinical outcomes in ER+ breast cancer patients with recurrence score 26-30-guided therapy: Real-world data

149P Clinical outcomes in ER+ breast cancer patients with recurrence score 26-30-guided therapy: Real-world data

Appraising Adjuvant Endocrine Therapy in Hormone Receptor Positive HER2-Negative Breast Cancer-A Literature Review.

Background: Approximately 75% of breast cancer (BC) is associated with luminal differentiation expressing endocrine receptors (ER). For ER+ HER2− tumors, adjuvant endocrine therapy (ET) is the cornerstone treatment. Although relapse events steadily continue, the ET benefits translate to dramatically lengthen life expectancy with bearable side-effects. This review of ER+ HER2− female BC outlines suitable adjuvant treatment strategies to help guide clinical decision making around appropriate therapy. Methods: A literature search was conducted in Embase, Medline, and the Cochrane Libraries, using ER+ HER−, ET BC keywords. Results: In low-risk patients: five years of ET is the standard option. While Tamoxifen remains the preferred selection for premenopausal women, AI is the choice for postmenopausal patients. In the high-risk category: ET plus/minus OFS with two years of Abemaciclib is recommended. Although extended ET for a total of ten years is an alternative, the optimal AI duration is undetermined; nevertheless an additional two to three years beyond the initial five years may be sufficient. In this postmenopausal group, bisphosphonate is endorsed. Conclusions: Classifying the risk category assists in deciding the treatment route and its optimal duration. Tailoring the breadth of ET hinges on a wide array of factors to be appraised for each individualized case, including weighing its benefits and harms.

SY30-4 Developmental therapeutics post CDK4/6 inhibitors

CDK 4/6 inhibitors have become the gold standard treatment in advanced hormone receptor (HR)-positive HER2-negative breast cancer; abemaciclib has also been approved for use in the adjuvant setting for certain high risk cancers recently. However, resistance to CDK 4/6 inhibition is an important challenge. With the uncovering of mechanisms of resistance, current clinical trials are focusing on different pathways: various tyrosine kinase receptors such as FGFR, ERBB2, PI3K-Akt, MAPK, and other cell cycle mediators.

RB loss determines selective resistance and novel vulnerabilities in ER-positive breast cancer models.

The management of metastatic estrogen receptor (ER) positive HER2 negative breast cancer (ER+) has improved; however, therapeutic resistance and disease progression emerges in majority of cases. Using unbiased approaches, as expected PI3K and MTOR inhibitors emerge as potent inhibitors to delay proliferation of ER+ models harboring PIK3CA mutations. However, the cytostatic efficacy of these drugs is hindered due to marginal impact on the expression of cyclin D1. Different combination approaches involving the inhibition of ER pathway or cell cycle result in durable growth arrest via RB activation and subsequent inhibition of CDK2 activity. However, cell cycle alterations due to RB loss or ectopic CDK4/cyclin D1 activation yields resistance to these cytostatic combination treatments. To define means to counter resistance to targeted therapies imparted with RB loss; complementary drug screens were performed with RB-deleted isogenic cell lines. In this setting, RB loss renders ER+ breast cancer models more vulnerable to drugs that target DNA replication and mitosis. Pairwise combinations using these classes of drugs defines greater selectivity for RB deficiency. The combination of AURK and WEE1 inhibitors, yields synergistic cell death selectively in RB-deleted ER+ breast cancer cells via apoptosis and yields profound disease control in vivo. Through unbiased efforts the XIAP/CIAP inhibitor birinapant was identified as a novel RB-selective agent. Birinapant further enhances the cytotoxic effect of chemotherapies and targeted therapies used in the treatment of ER+ breast cancer models selectively in the RB-deficient setting. Using organoid culture and xenograft models, we demonstrate the highly selective use of birinapant based combinations for the treatment of RB-deficient tumors. Together, these data illustrate the critical role of RB-pathway in response to many agents used to treat ER+ breast cancer, whilst informing new therapeutic approaches that could be deployed against resistant disease.

Results of the safety run-in of gedatolisib plus talazoparib in advanced triple negative or BRCA 1/2 positive HER2 negative breast cancer.

e13075 Background: Metastatic triple negative breast cancer (TNBC) is a disease subtype with a poor prognosis, though advancements have been made in the use of targeted therapies, such as poly (ADP-ribose) polymerase inhibitors (PARPi) for those with germline BRCA 1/2 mutations. Up to 2/3 of TNBC tumors have acquired defects in homologous recombination (HR) DNA repair, yet PARPi monotherapy has been ineffective in extending survival in these patients. Phosphoinositide-3-kinase (PI3K)/mTOR pathway alterations are also common, and preclinical data supports that PI3K/mTOR inhibition may disrupt normal function of the HR complex and increase dependency on PARP enzymes for HR DNA repair. Thus, combining a PI3K/mTORi with a PARPi may result in a synergistic anti-neoplastic effect. Methods: The safety run-in portion of this study evaluated the safety and preliminary efficacy of the combination of weekly IV gedatolisib (PI3K/mTORi) and continuous daily talazoparib. Germline BRCA mutations were not required. The safety run-in was designed to determine the maximum tolerated dose (MTD) and recommended phase 2 dose (RP2D). A 3+3 design was utilized for dose escalation, with starting dose at level 1. Dose levels are as shown in the Table. Eligibility criteria included patients ≥ age 18 who had received 1-3 prior lines of therapy for advanced TNBC or advanced HER2-negative BC with a germline BRCA 1/2 mutation. Those with untreated CNS metastasis were excluded as were those type I diabetes or uncontrolled type II diabetes, due to the risk of hyperglycemia with gedatolisib. Results: A total of 14 female patients were enrolled on to the safety run-in phase of the trial. Median age was 53 (range 30-67). Most patients (79%) were Caucasian, 14% were African American, and 7% unknown. The most common adverse events (AEs) of any grade were fatigue, anemia, nausea, and oral mucositis. Grade 1 hyperglycemia was noted in about 1/3 of the cohort, with 1 grade 3 event. There were 3 patients who experienced grade 4 AEs, thrombocytopenia (2) and lymphopenia (1). There was 1 DLT of grade 3 neutropenia which occurred at dose level 1. The MTD of gedatolisib was 180 mg and MTD of talazoparib was 1 mg. In this preliminary cohort, 3 patients achieved PR and 5 patients achieved SD. Median duration of PR was 13.34 months and median duration of SD was 4.11 months. Of the 3 patients with a BRCA 1 or 2 mutation, 2 had a best response of PR and the other SD. Conclusions: The safety run-in indicated that this combination is safe and well tolerated with mostly grade 1-2 AEs. This combination therapy has moved into the phase II trial, with 2 cohorts. Cohort A includes BRCA-wildtype patients with TNBC and cohort 2 includes those with a BRCA mutation and HER2-negative disease. Clinical trial information: NCT03911973. [Table: see text]