Abstract P3-05-20: Low 21-Gene Recurrence Score Is Not Associated with a High Axillary Nodal Burden in Post-Menopausal Women Presenting with a Clinically Negative Axilla

Abstract Background: The predictive and prognostic value of the 21-gene recurrence score (RS) has emphasized the importance of tumor biology and minimized the credence of a limited (1-3 positive) nodal burden. The practice changing results of RxPonder demonstrated that post-menopausal women with 1-3 positive lymph nodes (pN1) and a RS of ≤25 did not necessarily benefit from adjuvant chemotherapy. Given that RS influences adjuvant therapy decision-making more significantly than nodal status, it is unclear whether axillary staging with sentinel lymph node biopsy (SLNB) has a continued role in the surgical care of post-menopausal patients otherwise presenting with early stage, clinically node negative (cN0) hormone receptor positive (HR+), human epidermal growth factor receptor 2 negative (HER2-) invasive breast cancer. In this context, the de-escalation of axillary staging, especially in the presence of a low RS, is an area of active investigation. To help elucidate this further, we sought to estimate the association of RS with pathologic nodal stage. Methods: Using the 2004-2019 National Cancer Database (NCDB) Patient User File (2022 release), we evaluated the association of RS with the incidence of pN0, pN1 and pN2-3 disease. Only female patients diagnosed who were age 50 and older with HR+/HER2- invasive breast cancer were eligible, and only those presenting with cT1-T2N0 who underwent upfront surgery with a SLNB comprised our study population. Those with Oncotype DX testing performed with an available RS were included. Given the limitations within the dataset, age 50 and over was selected as a surrogate for post-menopausal status. Categorical variables were compared between RS groups (≤25 vs. >25) using chi-square tests and continuous variables were compared using t-tests. A logistic regression analysis was performed to estimate the association between RS (≤25 vs. >25) and nodal burden (pN2-3 vs pN0-1). Results: There were 151,447 patients with an invasive breast cancer diagnosis between 2015 and 2019 who met inclusion criteria. The average age at diagnosis was 64.1 (IQR 58-69) and almost 75% of tumors displayed ductal histology. There were 130,568 (86.2%) patients with a RS≤25 and 20,879 (13.8%) with a RS >25. On final pathology, 85.2% were pN0 and 14.8% were pN1-3. For those with a RS ≤25, 84.9% were pN0, 14.8% were pN1 and 0.3% were pN2-3. For those with a RS >25, 86.8% were pN0, 12.9% were pN1 and 0.3% were pN2-3. Overall, 14.5% demonstrated pN1 disease, of which 12.3% yielded a RS >25. Of the 461 patients with pN2-3 disease for whom RS was available, 12.4% (57 patients) had RS >25. After adjustment, RS >25 was associated with reduced incidence of pN2-3 compared to pN0-1 (OR=0.64, 95% CI 0.47-0.87, p=0.004). Conclusion: In this population of post-menopausal patients with cT1-T2N0, HR+/HER2- invasive breast cancer and an available RS, almost 86% displayed pN0 or pN1 disease in conjunction with a RS ≤25. Based on the current available literature, less than 5% of cT1-2N0 patients are thought to harbor >pN1 disease. These data add further support, suggesting that this patient population is unlikely to harbor a higher than limited nodal burden given a clinically negative axilla. Though less than 0.5% of the studied patient population demonstrated pN2-3 disease, an important caveat to make is that these patients would not have met criteria for RS, and it’s likely this low number reflects the absence of testing. Given that RS has not been validated for this higher nodal stage, we cannot make recommendations to omit axillary surgery in this cohort of patients. The data presented here provides further rationale for the two large prospective studies addressing whether SLNB could be eliminated in patients with otherwise small HR+/HER2- tumors which are currently ongoing. Table 1: Pathologic Nodal Staging Based on Recurrence Score Citation Format: Astrid Botty van den Bruele, Morgan Paul, Samantha M. Thomas, Sarah L. Sammons, Maggie L. DiNome, Jennifer K. Plichta, Akiko Chiba, Laura H. Rosenberger, E Shelley Hwang. Low 21-Gene Recurrence Score Is Not Associated with a High Axillary Nodal Burden in Post-Menopausal Women Presenting with a Clinically Negative Axilla [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P3-05-20.