Hormone Receptor Positive HER2 Research Articles

Immune environment of high-TIL breast cancer: triple negative and hormone receptor positive HER2 negative

This study explores differences in immune cell (IC) composition and spatial distribution between triple-negative breast cancer (TNBC) and hormone receptor-positive, HER2-negative breast cancer (HR + HER2-BC) in high-TIL (≥60%) cases, focusing on PD-L1 status. Using multiplex immunofluorescence on resected tumor tissues from 18 TNBC and 14 HR + HER2-BC cases, we analyzed IC types (CD20, CD8, CD4, FOXP3) and their spatial interactions. TNBC showed a unique IC composition characterized by a higher proportion of CD8 + IC (stroma: 27% vs 17%, p < 0.001; tumor: 54% vs 31%, p < 0.001) and CD4 + FOXP3 + IC (stroma: 3.9% vs 3.0%, p = 0.036), compared to HR + HER2-BC. Notably, PD-L1 positive TNBC cases demonstrated denser infiltration CD4 + FOXP3 + IC in the stromal region compared to HR + HER2-BC (146.4 ± 67.1/mm2 vs 114.3 ± 146.9/mm2, p = 0.036), along with pronounced IC clustering near TC. Both tumor subtypes displayed varied IC compositions based on PD-L1 status. In conclusion, IC composition and spatial distribution in high-TIL TNBC and HR + HER2-BC significantly differ, influenced by PD-L1 status.

Populations of Triple Negative and Hormone Receptor Positive HER2 Negative Breast Tumors Share Immune Gene Profiles

Background: Immune therapy has revolutionized the treatment of certain cancers including melanoma and lung cancer. Breast cancer has fewer tumors with high immune infiltrate and Immune Checkpoint Inhibitor (ICI) therapy has shown the most significant responses in the Triple Negative (TN) subtype although roles are emerging in the other subtypes. The presence of Tumor Infiltrating Lymphocytes (TIL) is predictive of response to ICI therapy in metastatic TN and associated with better survival in local TN disease. Hormone Receptor (HR) positive HER2 negative (HR+HER2-) breast tumors do not show improved prognosis with increasing TIL and only a small portion of HR+HER2- tumors respond to ICI in both metastatic and local disease. We therefore sought to identify genetic differences between TN and HR+HER2- tumors to identify how these may contribute to their differences in immune infiltrate. Methods: We contrasted immune-associated gene expression between 119 TN and 475 HR+HER2- breast tumors from The Cancer Genome Atlas (TCGA) and confirmed our findings from 299 TN and 1369 HR+HER2- breast tumors in METABRIC. Results: We found that TN and HR+HER2- tumors can be grouped into immune-high or -low tumors, with both subtypes represented in the immune-high group (40% HR+HER2- tumors of both Luminal A and Luminal B type and 71% TN tumors) in the TCGA. The genes upregulated in the immune-high cluster included GZMB, CXCL9, and IDO1 (Log2FC &gt; 2; Adj. p &lt; 10X10-40). The largest expression difference between the immune-high TN and HR+HER2- tumors was that TN tumors had more abundant Th1 and Th2 CD4+ T cells while HR+HER2- tumors had more abundant fibroblasts (Log2FC &gt; 0.3; Adj p &lt; 10X10-10). Conclusions: Our data suggest that an immune-high signature is not dictated by breast cancer subtype. However, fibroblasts, particularly fibroblast subsets associated with worse outcome, are more abundant in the immune-high HR+HER2- tumors.

Populations of triple negative and hormone receptor positive HER2 negative breast tumors share immune gene profiles.

In breast cancer, triple negative (TN) breast cancer has most responses to immune checkpoint inhibitor (ICI) therapy. Lymphocyte infiltrate does not impact prognosis in Hormone receptor positive HER2 negative (HR + HER2-) breast tumors and few HR + HER2- tumors respond to ICI. We contrasted immune-associated gene expression between 119 TN and 475 HR + HER2- breast tumors from The Cancer Genome Atlas (TCGA) and confirmed our findings in 299 TN and 1369 HR + HER2- breast tumors in the METABRIC database. TN and HR+ HER2- tumors grouped into immune-high or -low tumors, both subtypes were represented in the immune-high group. The largest difference between the immune-high TN and HR + HER2- tumors was TN tumors had more abundant Th1 and Th2 CD4+ T cells while HR + HER2- tumors had more abundant fibroblasts (log2FC > 0.3; p < 10×10-10). This suggests an immune-high signature is not dictated by breast cancer subtype, but fibroblast subsets associated with worse outcome were higher in the immune-high HR + HER2- tumors.

Cancer outcomes from a real-world cohort of patients eligible for adjuvant CDK4/6 inhibitors but without genomic risk for chemotherapy: A GBECAM multicenter retrospective study.

540 Background: In the MonarchE and Natalee studies, most patients received (neo)adjuvant chemotherapy (CT). In the precision oncology era, genomic signatures such as Oncotype DX (ODX) can spare many patients of CT. Our recent Real-World data (RWD) showed that a proportion of patients with hormone receptor positive (HR+) HER2 negative (HER2-) early breast cancer (eBC) would be eligible for adjuvant abemaciclib or ribociclib without genomic indication for CT. The main question addressed in this analysis is the potential benefit of adjuvant CDK4/6i in the non-CT eligible population; for this, we evaluated cancer recurrence outcomes of these patients. Methods: This is a multicentric RWD study derived from a large dataset of patients with T1-T3, N0-N1, HR+/HER2- eBC who had an ODX performed between 2005 and 2020 and were treated across nine Brazilian institutions. Projections of CT indication by genomic criteria were based on TAILORx and RxPONDER data. Projections of adjuvant CDK4/6i indication were based on the MonarchE and Natalee inclusion criteria. Primary endpoints were 4-year invasive disease-free survival (4-yr iDFS) and 4-year distant disease-free survival (4-yr DDFS) rates in the cohort of patients potentially eligible for CDK4/6i without genomic indication for CT and who did not receive adjuvant CT in the clinical practice. Results: Of 636 patients, the ODX indicated low (&lt;11), intermediate (11-25) and high (&gt;25) genomic risk in 117 (18.4%), 408 (64.1%) and 111 (17.5%) patients, respectively. 408 patients (64.2%) had low clinical risk and 228 patients (35.8%) had high clinical risk disease. In the overall cohort, 12 (1.8%) and 67 (10.5%) pts were eligible for adjuvant abemaciclib and ribociclib, respectively, without having received adjuvant CT (both by genomic indication and clinical practice). In patients with indication of abemaciclib (median follow-up [FU] of 23 months; a maximum of 114 months), 4-yr iDFS and 4-yr DDFS rates were both 100%. In patients with indication of ribociclib (median follow-up of 33 months; a maximum of 127 months), 4-yr iDFS and 4-yr DDFS rates were both 100%. In the entire cohort, there was only one distant recurrence event, at 96 months after diagnosis, in a 55-year-old patient with stage IIB (T2N1) eBC and low genomic risk (RS=11). Conclusions: In times of rapid incorporation of both GES and adjuvant CDK4/6i, our results suggest that patients eligible for adjuvant abemaciclib and/or ribociclib in the non-CT population have a favorable short-term outcome with endocrine therapy alone. Therefore, additional data and longer follow-up are needed to clarify the role of these costly and potentially toxic agents in patients spared CT by genomic signatures.

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&lt;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 &lt;11 (n=17; r=0.2415; p=0.3504), Oncotype ≤18 (n=43; r=0.0914; p=0.5600), Oncotype &lt;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.

Association of circulating T lymphocytes and their functional states with pathologic complete response (pCR) in breast cancer (BC). A prospective Italian study.

559 Background: In BC, pCR is associated with substantial survival benefit. Hence, escalated neoadjuvant treatments (NATs) are being increasingly employed to improve pCR rates, warranting biomarkers for better patients’ selection. T-cell exhaustion and senescence are dysfunctional states that coexist in patients with cancer, impairing antitumor immunity and sustaining a suppressive immune microenvironment. Here, we assessed the impact of such states on pCR across different BC subtypes and NATs. Methods: This is a prospective study on patients undergoing NAT for BC at the Maggiore Hospital of Novara, Italy. Blood was collected at baseline and after NAT. Circulating T lymphocytes were characterized with exhausted (CD28, PD1, LAG3) and senescent (CD57, KLRG-1) biomarkers utilizing flow cytometry. Neutrophiles/lymphocytes ratio (NLR) and lymphocytes/monocytes ratio (LMR) were also retrieved. Subpopulations with frequency &lt;1% were normalized for total CD3+ cells. Results: From October 2020 to January 2024, 134 patients were enrolled and 115 completed NAT (85.8%). Fifty-one (38,1%) had adequate samples for analysis, 16 (31,4%) with hormone receptor positive HER2 negative BC (HR+HER2-), 15 (29,4%) with HER2+, and 20 (39,2%) with triple negative BC (TN). At baseline, patients with TNBC had the lowest NLR (p=0.018) and lowest senescent CD4+CD28- (p=0.042). Associations with pCR are shown in the Table. Overall, LMR associated with increased pCR (OR 1.34 [95% CIs 1.00-1.89]), and NLR with decreased pCR (OR 0.67 [0.39-1.04]). Both associations were driven by HR+ status (interaction p = 0.061 and 0.060). Senescent CD4+ predicted lower pCR in both HR-HER2+ (OR 0.10 [0.01-0.36]) and TNBC (OR 0.10 [0.01-0.5]). In TNBC, exhausted CD8+ predicted higher pCR (OR 1.78 [1.08-3.79]). When assessed separately in patients who received NAT with or without pembrolizumab, exhausted CD8+ remained predictor of pCR in chemotherapy + pembrolizumab (OR 1.84 [1.03-5.00]), but not with chemotherapy alone (p=0.203). The dynamics of paired pre-NAT and post-NAT TNBC samples revealed significant differences. Senescent CD4+ increased after chemotherapy, but not with chemotherapy + pembrolizumab (p=0.007). Pembrolizumab was associated with depletion of PD1-positive CD8+, while chemotherapy alone was not (p=0.020). Conclusions: The characterization of circulating T lymphocytes could help identify patients who benefit more in terms of pCR from specific NATs, including chemoimmunotherapy. [Table: see text]

Abstract PO3-18-06: First-in-human phase 1A study of RGT-419B, a next generation CDK4 inhibitor, in patients (pts) with hormone receptor positive (HR+) HER2- advanced/metastatic breast cancer (ABC) who progressed on prior CDK4/6 inhibitors (CDK4/6i)

Abstract Introduction: RGT-419B is a novel next generation CDK inhibitor. It has high potency against CDK4 with additional activity against CDK2 and selectivity against CDK6 to overcome resistance and reduce hematologic toxicity. In addition to anti-cancer activity in preclinical breast cancer models that are resistant to approved CDK4/6 inhibitors, we report the interim data from the first-in-human, multicenter trial of RGT-419B as a single agent in post-menopausal pts with HR+ HER2- ABC. Methods: Eligible pts received ≥2 lines of treatment and progressed on endocrine therapy (ET) and at least 1 line of an FDA approved CDK4/6i. Prior treatments of fulvestrant, other targeted agents and/or chemotherapy were allowed. Dose escalation of RGT-419B as oral (PO) monotherapy was administered in continuous 28-day cycles in 4 cohorts (25, 75,150 mg QD and 150 mg BID). A standard 3+3 design was employed to determine the maximum tolerated dose (MTD)/recommended dose for expansion (RDE). The primary objective was to assess safety and tolerability. The secondary objectives included pharmacokinetic (PK) assessment and exploratory efficacy. Results: At time of abstract submission, 12 eligible post-menopausal pts with HR+/HER2- ABC received RGT-419B. The median age was 64.8y (range 50-80y). All had prior palbociclib + ET (2 pts had abemaciclib or ribociclib after palbociclib); a majority received fulvestrant (67%) and prior chemotherapy (50%). Across the 4 cohorts (12 pts), the most observed treatment-emergent adverse events (TEAEs; all causality) with RGT-419B were nausea, reduced white blood cell counts (neutrophils and/or lymphocytes) and diarrhea. At data cutoff on June 30th 2023, there have been no CTCAE Grade 3 or higher treatment related AE (TRAEs). No ocular toxicity has been observed. No pts have discontinued treatment due to RGT-419B toxicity. Preliminary PK analyses for RGT-419B showed a dose-dependent increase of exposure at steady state with long half-life. Tumor assessments (RECIST v1.1) of pts in the first 3 cohorts treated with RGT-419B monotherapy (25-150 mg QD) showed partial responses in 2 pts (7 pts with measurable disease), 28.6% partial response (PR) (RECIST v. 1.1) and clinical benefit rate (CBR) 44%. Updated safety, PK and efficacy data will be presented. Conclusions: RGT-419B, with potent selective CDK4 activity, CDK2 activity and CDK6 selectivity, demonstrated a favorable safety and PK profile in an ongoing phase I study, with no grade 3 or higher TRAEs observed thus far. RGT-419B administered as once daily monotherapy also demonstrated preliminary evidence of efficacy as well. Dose expansions of RGT-419B as a single agent and in combination with ET in pts with HR+/HER2- ABC following prior CDK4/6i progression are planned. Citation Format: Seth Wander, Dave Valacer, Richard Zuniga, Heather Yeckes-Rodin, Christopher Perkins, Lisa Ge, Lili Yao, Jing Lin, Dawn Begley, Feifei Sun, Andie Zheng, Jing Han, Zhi (Julie) Xie, Aditya Bardia, Kevin Kalinsky. First-in-human phase 1A study of RGT-419B, a next generation CDK4 inhibitor, in patients (pts) with hormone receptor positive (HR+) HER2- advanced/metastatic breast cancer (ABC) who progressed on prior CDK4/6 inhibitors (CDK4/6i) [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 PO3-18-06.

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&amp;gt;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&amp;gt;26. Methods: Pts with ER+/HER2- BC and RS&amp;gt;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 &amp;gt;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 PS05-06: Outcomes of Surveillance using Contrast Enhanced Mammography in Women with a Personal History of Breast Cancer

Abstract Background Women with a personal history of breast cancer (PHBC) have a high rate of subsequent breast malignancy. Annual mammography with selective ultrasound has been the standard method of surveillance after breast cancer for many years, aiming for early detection, treatment and improved survival. In surveillance populations, interval cancers, which can account for ~30% of subsequent breast cancers, are more likely to be larger, hormone receptor negative and lymph node positive than cancers detected by surveillance (Lee et al, Radiology 2021). Interval cancer rates of 3.6 per 1000 mammographic screens have been reported previously in women with PHBC (Houssami et al, JAMA 2011). For women with PHBC a more sensitive surveillance approach may be justified, noting mammography has lower program sensitivity in PHBC surveillance than in screening. Magnetic resonance imaging (MRI) is used selectively but with resource and access limitations. Contrast enhanced mammography (CEM) offers a more sensitive modality than conventional mammography with specificity comparable to MRI, but its utility for surveillance is uncertain. Methods Retrospective study of 1,190 women with PHBC who commenced annual CEM surveillance in an Australian hospital setting between June 2016 and December 2022 (Elder et al, Breast Cancer Res Treat 2023) combining outcomes of initial CEM and any subsequent surveillance imaging over that period, including incident surveillance-detected cancers and interval cancers (cancers diagnosed in the year following a negative surveillance episode), recalls for assessment, the contribution of contrast to recall, and pathology and treatment details for cancer diagnoses. Outcomes were reported using descriptive statistics and hazards modelling. Results There were 3,784 episodes for analysis: 1,190 first CEM surveillance episodes, and 2,594 subsequent surveillance episodes of which &amp;gt;90% were contrast based imaging. 79% of women had at least three annual rounds of surveillance imaging. 186 cases from the total 3784 surveillance episodes were recalled for assessment (recall rate 4.9%). 72 (39%) recalled cases identified malignant lesions (true positives (TP)), with 50 invasive cancers and 22 cases of DCIS. 114 (61%) recalled cases were false positives (FP). 51% of cases were only recalled due to contrast and 35% of these were TP. Invasive cancers were predominantly stage 1 (64%) or stage 2 (32%) and most were grade 2 (44%) or grade 3 (47%). The median invasive cancer size was 16mm (IQR 9-25mm). 62% of invasive cancers were hormone receptor positive HER2 negative, and 24% were triple negative. The median DCIS size was 19mm (IQR 10-26mm) with only a single low grade case. 40% of invasive cancers and 59% of DCIS were recalled due to contrast. Comparison of tumour features indicates similarities between contrast-directed recalls and other diagnoses; conclusive findings would require a larger sample. Five interval cancers were identified, of which three were asymptomatic and detected on surveillance imaging scheduled early for other reasons. Thus, the rate of symptomatic interval cancers was 0.8 per 1000 screens (program sensitivity 96.0%). Surveillance-detected cancer rates differed significantly by index cancer subtype (χ2=11.9, p=0.0026), with highest rates for women with triple negative index cancers. Incidence cancer rates were higher among the 6.9% of women with moderate or marked BPE at first CEM surveillance episode (χ2=8.8, p=0.032), but did not differ significantly by age group (χ2=5.2, p=0.39) nor breast density (χ2=4.7, p=0.19). Conclusions Routine use of CEM in annual surveillance of women with PHBC led to 1.85-fold increase in the detection of clinically significant malignant lesions, with lower interval cancer rates than previous published series of women with PHBC. CEM appears to increase the sensitivity of surveillance programs for women with PHBC, improving on imaging without contrast. Citation Format: Julia Matheson, Carolyn Nickson, Kenneth Elder, Allan Park, Allison Rose, Bruce Mann. Outcomes of Surveillance using Contrast Enhanced Mammography in Women with a Personal History of 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 PS05-06.

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 PO2-04-09: Combination of the PLK1 Inhibitor Onvansertib and the PI3Kα Inhibitor Alpelisib Overcomes Palbociclib Resistance in PIK3CA-mutated HR+ Breast Cancer

Abstract In the 1st line setting of hormone receptor-positive HER2 negative (HR+/HER2-) metastatic breast cancer, cyclin dependent kinase 4 and 6 (CDK4/6) inhibitors (palbociclib, abemaciclib and ribociclib) are typically used in combination with endocrine therapy. Though initially effective, acquired resistance to either CDK4/6 inhibitors or endocrine therapy eventually leads to disease relapse in most patients. Activating mutations in PIK3CA, the gene encoding alpha catalytic subunit of phosphatidylinositol-4,5-bisphosphat 3-kinase (PI3K) are found in approximately 40% of HR+ breast cancer patients and have been implicated in mediating resistance to CDK4/6 inhibitors. The PI3Kα inhibitor alpelisib is currently approved for PI3KCA-mutant HR+ breast cancer after progression on CDK4/6 inhibitors. However, drug-associated resistance mechanisms may limit its clinical benefit. Synergistic combination therapies have the potential to improve efficacy and overcome resistance mechanisms. Polo-like kinase 1 (PLK1) is a serine-threonine-protein kinase, key cell cycle regulator that controls G2/M entry and mitotic progression, and that has been shown to mediate resistance to palbociclib in HR+ breast cancer. Onvansertib is an oral and highly specific PLK1 inhibitor currently on clinical development in solid tumors and hematological malignancies. Here we evaluated the potential of onvansertib to increase the activity of alpelisib in PIK3CA-mutant HR+ breast cancer preclinical models. The combination of onvansertib and alpelisib synergistically inhibited cell viability and/or colony formation in three PI3KCA-mutant HR+ breast cancer cell lines, MCF-7 (PIK3CA E545K), EFM-19 (PIK3CA H1047L), and T-47D (PIK3CA 1047R). A significant increase in apoptosis was observed in cells treated with the combination compared to either agent alone. We next tested the combination of onvansertib and alpelisib in patient-derived xenograft (PDX) models. For this purpose, palbociclib-resistant PIK3CA-mutant HR+ breast cancer PDXs were established from primary breast tumor (PDX HBCx-86, PIK3CA E545K) or from metastatic bone biopsies of patients who had progressed on endocrine therapy plus palbociclib (HBCx-180, PIK3CA H1047R) or on PI3Kα inhibitor (HBCx-134palboR31, PIK3CA H1047R). PDX tumors were grafted subcutaneously in nude mice and mice were treated with vehicle, onvansertib (45 mg/kg, oral, 5 days a week), alpelisib (25mg/kg, oral, 5 days a week) or the combination. The combination was well tolerated and showed superior anti-tumor activity than the single agents in the 3 PDX models. In the HBCx-86 PDX, although none of the single agents showed activity, the combination induced potent tumor growth inhibition. In the metastasis-derived PDX HBCx-134palboR31, the combination treatment induced pronounced tumor regression in 62% of mice (5/8), with complete response in 25% (2/8), while mice treated with the single agents showed tumor progression. Finally, in the HBCx-180 PDX, established from a patient with primary resistance to palbociclib, the efficacy of the combination was greater and more durable, with significant survival advantage, compared to the monotherapies. Collectively, our preclinical findings suggest that co-targeting PLK1 and PI3Kα with onvansertib and alpelisib respectively, may constitute a promising therapeutic combination strategy for patients with PIK3CA-mutant HR+ breast cancer failing to respond to first-line standard of care therapies. Citation Format: Sreeja Sreekumar, Pierre Painsec, Davis Klein, Dalia Gonzalez, Laura Sourd, Elodie Montaudon, Tod Smeal, Elisabetta Marangoni, Maya Ridinger. Combination of the PLK1 Inhibitor Onvansertib and the PI3Kα Inhibitor Alpelisib Overcomes Palbociclib Resistance in PIK3CA-mutated HR+ 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 PO2-04-09.

Outcomes of sentinel node biopsy according to MRI response in an association with the subtypes in cN1–3 breast cancer after neoadjuvant systemic therapy, multicenter cohort study

BackgroundThis study investigated the feasibility of sentinel lymph node biopsy (SLNB) after neoadjuvant systemic therapy (NAST) in patients with initially high nodal burden.MethodsIn the multicenter retrospective cohort, 388 individuals with cN1–3 breast cancer who underwent NAST and had SLNB followed by completion axillary lymph node dissection were included. In an external validation cohort, 267 patients with HER2+ or triple-negative breast cancer (TNBC) meeting similar inclusion criteria were included. Primary outcome was the false-negative rates (FNRs) of SLNB according to the MRI response and subtypes. We defined complete MRI responders as patients who experienced disappearance of suspicious features in the breast and axilla after NAST.ResultsIn the multicenter retrospective cohort, 130 (33.5%) of 388 patients were of cN2-3, and 55 (14.2%) of 388 patients showed complete MRI responses. In hormone receptor-positive HER2− (n = 207), complete and non-complete responders had a high FNRs (31.3% [95% CI 8.6–54.0] and 20.9% [95% CI 14.1–27.6], respectively). However, in HER2+ or TNBC (n = 181), the FNR of complete MRI responders was 0% (95% CI 0–0), whereas that of non-complete responders was 33.3% (95% CI 20.8–45.9). When we validated our findings in the external cohort with HER2+ or TNBC (n = 267), of which 34.2% were cN2-3, the FNRs of complete were 7.1% (95% CI 0–16.7).ConclusionsOur findings suggest that SLNB can be a reliable option for nodal status evaluation in selected patients who have responded well to NAST, especially in HER2+ and TNBC patients who show a complete MRI response.

Determinants of pathological complete response to neoadjuvant chemotherapy in breast cancer: A single-institution experience.

Neoadjuvant chemotherapy (NACT) is routinely used in all cases of locally advanced breast cancer and some cases of early breast cancer. We previously reported a pathological complete response (pCR) rate of 8.3%. With the increasing use of taxanes and human epidermal growth factor receptor 2 (HER2)-directed NACT, we conducted this study to understand the current pCR rate and its determinants. A prospective database of breast cancer patients who underwent NACT followed by surgery between January and December 2017 was evaluated. Of the 664 patients, 87.7% were cT3/T4, 91.6% were grade III, and 89.8% were node-positive at presentation (54.4% cN1, 35.4% cN2). The median age was 47 years; median pre-NACT clinical tumor size was 5.5 cm. Molecular subclassification was 30.3% hormone receptor positive (HR+) HER2-, 18.4% HR+HER2+, 14.9% HR-HER2+, and 31.6% triple negative (TN). Both anthracyclines and taxanes were given preoperatively in 31.2% patients whereas 58.5% of HER2 positive patients received HER2-targeted NACT. The overall pCR rate was 22.4% (149/664), 9.3% in HR+HER2-, 15.6% in HR+HER2+, 35.4% in HR-HER2+, and 33.4% in TN. On univariate analysis, duration of NACT ( P < 0.001), cN stage at presentation ( P = 0.022), HR status ( P < 0.001), and lymphovascular invasion ( P < 0.001) were associated with pCR. On logistic regression, HR negative status (Odds ratio [OR] 3.314, P < 0.001), longer duration of NACT (OR 2.332, P < 0.001), cN2 stage (OR 0.57, P = 0.012), and HER2 negativity (OR 1.583, P = 0.034) were significantly associated with pCR. Response to chemotherapy depends on molecular subtype and duration of NACT. A low rate of pCR in the HR+ subgroup of patients warrants reconsideration of neoadjuvant strategies.

The Treatment Landscape of Elderly Patients with Hormone Receptor-Positive Her2 Negative Advanced Breast Cancer: Current Perspectives and Future Directions.

Breast cancer (BC) in elderly women is an increasing health issue due to demographic changes. BC tends to present later and may receive less than standard treatment options. More often, BC in elderly patients is endocrine-positive (HR+). The treatment of elderly patients with metastatic BC (mBC) represents a therapeutic challenge. In recent years, the treatment landscape of patients that are HR+/Her2-negative has changed due to the introduction in clinical practice of new targeted drugs, which have improved patient outcomes. Elderly patients are a small percentage of all patients enrolled in clinical trials and, to date, there are no standardized guidelines that define the best treatment option for this patient population. This can lead to undertreatment or overtreatment, impacting patient morbidity and mortality. Geriatric Assessment tools to tailor the treatment in elderly patients are underused because they are long and difficult to apply in a busy routine clinical practice. For all these reasons, there is an urgent need to produce data about the best treatment for elderly patients with HR+ mBC. Herein, we report data from randomized clinical trials and real-world evidence on the therapeutic options for HR+ Her2-negative mBC elderly patients and explore future treatment directions.

MCM-2 Levels as a Potential Biomarker for Predicting High-Risk Breast Cancer Patients According to TAILORx Classification.

The minichromosome maintenance protein-2 (MCM-2) is a more sensitive proliferation marker than Ki-67. This study aimed to evaluate the relationship between MCM-2 and Oncotype DX recurrence score (ODX-RS) and determine an MCM-2 cutoff value in high-risk patients according to TAILORx risk categorization. Hormone receptor (HR) positive HER-2 negative early-stage breast cancer patients (pT1-2, pN0-N1, M0) who had ODX-RS were included in the study. According to the TAILORx trial, patients were divided into two groups with high (ODX-RS ≥26) and low risk (ODX-RS <26) in terms of ODX-RS. Formalin-fixed-paraffin-embedded tissues of patients were re-evaluated, and 3 µm sections were prepared for MCM-2 immuno-histochemical staining. The relationship between ODX-RS and the percentage of MCM-2 staining was evaluated in two groups. The ROC curve analysis was performed to determine the MCM-2 cut-off value for the TAILORx high-risk group (ODX-RS ≥26). The mean MCM-2 value was significantly higher in the high-risk group [(60.2 ± 11.2 vs 34.4 ± 13.8, p < 0.001)]. In the multivariate analysis, MCM-2 (OR: 1.27, 95% CI: 1.08-1.49, p = 0.003) and progesterone receptor (PR) levels ≤10% (OR: 60.9, 95% CI: 4.1-89.7, p = 0.003) were found to be independent factors indicating a high-risk group. A one-unit increase in MCM-2 level increased the likelihood of being in the high-risk group by 1.27 times. In the ROC curve analysis, the optimal MCM-2 cut-off level was 50 (AUC: 0.921, sensitivity: 86.7%, specificity: 96.0%, p < 0.001). Our study is the first study in the literature to investigate the relationship between ODX-RS and MCM-2 levels in HR-positive HER-2 negative early breast-cancer patients. In this study, MCM-2 was an independent risk factor in identifying high-risk patients according to TAILORx risk classification. MCM 2 cut-off value (50) may help the decision on adjuvant chemotherapy in patients where the Oncotype DX test cannot be performed.

Successful Breast Conservation After Neoadjuvant Chemotherapy in Lobular Breast Cancer: The Role of Menopausal Status in Response to Treatment.

While neoadjuvant chemotherapy (NAC) has been shown to increase rates of breast conservation surgery (BCS) for breast cancer, response rates in invasive lobular carcinoma (ILC) appear lower than other histologic subtypes. Some data suggest higher response rates to NAC in premenopausal versus postmenopausal patients, but this has not been studied in ILC. We evaluatedthe rates of successful BCS after NAC in patients with ILC stratified by menopausal status. We analyzed data from a single-institution cohort of 666 patients with stage I-III hormone receptor positive HER-2 negative ILC. We used t-tests, chi-squared tests, and multivariable logistic regression to investigate rates of NAC use, attempted BCS, and associations between NAC and successful BCS by menopausal status. In 217 premenopausal and 449 postmenopausal patients, NAC was used more often in the premenopausal group (15.2% vs. 9.8%, respectively, p = 0.041). Among those who attempted breast conservation (51.3% of pre- and 64.8% of postmenopausal cohorts), NAC was not associated with successful BCS in either group. Interestingly, for postmenopausal patients, receipt of NAC was significantly associated with increased rates of completion mastectomy in those who had positive margins at thefirst attempt at BCS. NAC was not associated with successful BCS in either premenopausal or postmenopausal patients with ILC. Although premenopausal patients were more likely to receive NAC, these data suggest that menopausal status may not be a good predictor of response to chemotherapy. Better predictors of response and more efficacious treatment for patients with ILC are needed.

Survival results according to Oncotype Dx recurrence score in patients with hormone receptor positive HER-2 negative early-stage breast cancer: first multicenter Oncotype Dx recurrence score survival data of Turkey.

The Oncotype Dx recurrence score (ODx-RS) guides the adjuvant chemotherapy decision-making process for patients with early-stage hormone receptor-positive, HER-2 receptor-negative breast cancer. This study aimed to evaluate survival and its correlation with ODx-RS in pT1-2, N0-N1mic patients treated with adjuvant therapy based on tumor board decisions. Estrogen-positive HER-2 negative early-stage breast cancer patients (pT1-2 N0, N1mic) with known ODx-RS, operated on between 2010 and 2014, were included in this study. The primary aim was to evaluate 5-year disease-free survival (DFS) rates according to ODX-RS. A total of 203 eligible patients were included in the study, with a median age of 48 (range 26-75) and median follow-up of 84 (range 23-138) months. ROC curve analysis for all patients revealed a recurrence cut-off age of 45 years, prompting evaluation by grouping patients as ≤45 years vs. >45 years. No significant difference in five-year DFS rates was observed between the endocrine-only (ET) and chemo-endocrine (CE) groups. However, among the ET group, DFS was higher in patients over 45 years compared to those aged ≤45 years. When stratifying by ODx-RS as 0-17 and ≥18, DFS was significantly higher in the former group within the ET group. However, such differences were not seen in the CE group. In the ET group, an ODx-RS ≥18 and menopausal status were identified as independent factors affecting survival, with only an ODx-RS ≥18 impacting DFS in patients aged ≤45 years. The ROC curve analysis for this subgroup found the ODx-RS cut-off to be 18. This first multicenter Oncotype Dx survival analysis in Turkey demonstrates the importance of Oncotype Dx recurrence score and age in determining treatment strategies for early-stage breast cancer patients. As a different aproach to the literature, our findings suggest that the addition of chemotherapy to endocrine therapy in young patients (≤45 years) with Oncotype Dx recurrence scores of ≥18 improves DFS.

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 &gt; 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.

EE512 Potential Long-Term Benefits of Extended Adjuvant Neratinib in Patients with High-Risk Hormone Receptor Positive (HR+) HER2+ Early-Stage Breast Cancer (ESBC) Following Use of T-DM1 or Pertuzumab: A Population Effectiveness Model

Neratinib is an efficacious HER2-targeted agent for HER2+ ESBC, although its potential clinical benefits among the incident U.S. HR+ HER2+ high-risk ESBC patient population following use of T-DM1 or pertuzumab have not been quantified. Our objective was to estimate the long-term potential treatment benefits of neratinib in this target population.

The real-world modeling of benefits demonstrated in major clinical trials on 2 HR+/HER2− metastatic breast cancer treatment with CDK4/6 inhibitor in the US: PALOMA-2 and MONALEESA-3.

e13070 Background: This retrospective study addresses the question of whether real-world treatment with CDK4/6 inhibitors in combination with Endocrine Therapy (ET) for advanced hormone receptor positive (ER+) HER2 negative breast cancer yields similar benefits as reported by the major clinical trials: PALOMA-2 and MONALEESA-3. Methods: This study used the nationwide electronic health record-derived-Flatiron Health de-identified database to test the benefits demonstrated in major clinical trials on MBC patients under treatment with CDK4/6 + Letrozole (PALOMA-2) or CDK4/6 + Fulvestrant (MONALEESA-3). Regarding PALMOMA-2, a total of 1,774 patients with ≥ 3 months of follow-up received either CDK4/6 + Letrozole (n=1,277) or Letrozole alone (n=497) as the first line of treatment between February 3, 2015, and November 02, 2021. To test the benefits reported in MONALEESA-3, 1,187 patients are selected who were treated with either CDK4/6 + Fulvestrant (n=786) who received no or up to 1 line of prior ET or Fulvestrant alone (n=401). We conducted inverse probability weighting to balance the baseline demographic and clinical characteristics between patients in all subgroups. Kaplan-Meier method and Cox proportional hazards were used to test for the association of CDK4/6 treatment on rwPFS as the primary outcome and rwOS as the secondary outcome while adjusting for patient characteristics (e.g., age, race, ECOG PS value, health insurance, etc). Results: The real-world analysis of PALOMA-2 showed similar results as demonstrated in the clinical trials. The findings showed receiving CDK4/6 + Letrozole as the first-line treatment was associated with significantly longer median PFS compared to receiving Letrozole alone (28.3 vs 18 months; hazard ratio [HR], 0.57; 95% CI, 0.46–0.69; P &lt; 0.0001). Median OS was 56.5 months for the group with first line CDK4/6 + Letrozole and 50.4 months for the group with Letrozole alone (HR=0.76, 95% CI, 0.61–0.93, P-value = 0.01). Analysis of real-world practices of MONALEESA-3 also endorsed the results reported from the trial. Median PFS was 17.5 months for the group treated with CDK4/6 + Fulvestrant who received no or up to 1 line of prior ET, while it was about 14.3 months for patients treated with only Fulvestrant (HR=0.64, 95% CI, 0.52–0.80, P-value &lt; 0.0001). Consistent OS benefit was observed in patients treated with CDK4/6 + Fulvestrant compared to those treated with only Fulvestrant (44.72 vs 35.83 months; hazard ratio [HR], 0.70; 95% CI, 0.52–0.94; P &lt; 0.0001). Conclusions: Consistent with what was reported in major clinical trials: PALOMA-2 and MONALEESA-3, receiving CDK4/6 inhibitor plus endocrine therapy (Letrozole or Fulvestrant) was associated with improved progression free survival compared with patients treated with ET alone in this “real-world” population of patients with HR+/HER2− MBC.