The applicability of the 21-gene assay to inform chemotherapy benefit in lymph node–positive hormone receptor–positive male breast cancer.

e12509 Background: There are no studies focusing on the applicability of the 21-gene Oncotype Dx Recurrence Assay (RS) assay in predicting the benefit from chemotherapy in hormone receptor positive (HR+) Her2 negative (Her2-) lymph node positive(LN+) male breast cancers (BC). The aims of our study were to determine if chemotherapy administration based on RS in men with HR+Her2-LN+ BC impacted overall survival (OS). Methods: We conducted a retrospective cohort study on adult men and women with HR+ Her2-, 1-3 axillary LN + BC, with a valid oncotype DX RS assay, diagnosed between the years 2004-2020, using the National Cancer Database. RS risk categories were defined as low risk: 0-13, intermediate risk:14-25, and high risk: ≥26. Results: Higher RS (both as a continuous and categorical variable) was significantly associated with worse OS in males (p=0.003 continuous, p=0.006 categorical), females ≤50 years old (p<0.001 both continuous and categorical), and females >50 years old (p<0.001 both continuous and categorical). In the stratified unadjusted and adjusted models (adjusted for race, lympho-vascular invasion, comorbidities, tumor grade, and year of diagnosis), there was no association between receipt of chemotherapy and OS in males for all RS groups. Conversely, chemotherapy improved the survival for women ≤50 years old who belonged to the intermediate and high RS risk groups (p=0.01 and p<0.001 respectively) and also improved OS for females >50 in all RS risk groups (p<0.001 for each of the three risk groups). Conclusions: RS is associated with OS in men and women with HR+ Her2- LN+ BC. However, RS is not an indicator of the benefit of chemotherapy on OS in men, in contrast to women, with HR+ Her2- LN+ BC.