Abstract P4-02-17: Impact of low hormone receptor expression on neoadjuvant chemotherapy response and patterns of care in early-stage HER2-negative breast cancer: a US National Cancer Database analysis

Abstract Background: Hormone receptor (HR) low (1-10%) HER2-negative breast cancer (BC) is emerging as a distinct subtype with similarities in clinical outcomes to triple-negative BC. However, there is a lack of consensus on treatment recommendations for chemo-immunotherapy and endocrine therapy in this subset. Here, we present results from a US National Cancer Database (NCDB) analyses of patients with HER2-negative BC evaluating response to neoadjuvant chemotherapy (NAC) and patterns of care by HR expression. Methods: Patients with stage I-III HER2-negative BC diagnosed in 2018 were identified in NCDB, a nationwide oncology outcomes database in the US. Quantitative HR expression was unavailable prior to 2018. Data were categorized into four groups by estrogen receptor (ER) and progesterone receptor (PR) expression: ER< 1% & PR< 1% (HR-Neg), ER 1-10% and/or PR 1-10% (HR-Low), ER >11-30% and/or PR>11-30% (HR-Int), ER> 30% and/or PR > 30% (HR-High). Those with undocumented HR status (3%) or without curative intent surgery (5%) were excluded. The primary outcome was pathologic complete response (pCR) by HR expression in those undergoing neoadjuvant chemotherapy. Key secondary objectives included assessment of clinicopathologic characteristics and practice patterns. The categorical variables were compared between the four groups using a Chi-square test. Age was compared using a Kruskal-Wallis test. Results: Out of 104,205 incident cases, 2541 (2.4%) were HR-Low and 1241 (1.2%) were HR-Int. Significant differences were found between HR groups with higher grade, clinical stage, and Ki-67 in HR-Low vs. HR-Int or HR-High groups (Table 1). Patients with HR-Low and HR-Int BC were more likely to receive chemotherapy than HR-High (74%, 70% vs. 20%; p < 0.001) and the use of adjuvant endocrine therapy correlated with HR expression. Only half of patients in the HR-Low group received any endocrine therapy compared to higher rates in the HR-Int and HR-High groups (52% vs. 74%, 92%; p< 0.001). pCR rates in those receiving neoadjuvant chemotherapy were significantly different by HR status, with higher pCR rates in HR-Low vs. HR-High groups (p< 0.001) (Table 2). NAC utilization significantly differed between groups. A higher proportion of patients with HR-Low BC received NAC than other HR-positive groups (p < 0.001). Additionally, there was an increased use of NAC in patients with HR-Low BC treated at academic vs. community cancer centers (p< 0.001). Conclusions: This is one of the largest real-world analyses comparing key differences in biology and practice patterns of HR-Low, HER2-negative BC. Consistent with prior studies, we report HR-Low BC to be a rare and distinct subtype with higher pCR rates compared to HR-High BC. Practice patterns show wide variability in utilization of neoadjuvant chemotherapy and endocrine therapy for these patients. Future studies should address this disparity and enhance representation of patients with HR-Low BC in clinical trials to improve long-term outcomes. Table 1: Patient demographics Table 2: Neoadjuvant chemotherapy response amongst differing HR expression levels Citation Format: Dionisia Quiroga, Michael Grimm, Julie Stephens, Kai Johnson, Nicole Williams, Preeti K. Sudheendra, Mathew A. Cherian, Daniel Stover, Ashley C. Pariser, Margaret Gatti-Mays, Robert Wesolowski, Jose G. Bazan, Sasha Beyer, Ko Un Park, Bridget Oppong, Bhuvaneswari Ramaswamy, Julia White, Sachin R. Jhawar, Sagar Sardesai. Impact of low hormone receptor expression on neoadjuvant chemotherapy response and patterns of care in early-stage HER2-negative breast cancer: a US National Cancer Database analysis [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P4-02-17.