Tumor grade and progesterone receptor status in predicting benefit of chemotherapy in high genomic risk breast cancer

Background Not all eligible breast cancer (BC) patients could afford the expensive test of 21-gene recurrence score (RS) assay. This study aimed to identify clinicopathological factors associated with high-risk RS and examine whether these factors correlate with the benefit of chemotherapy. Research design and methods Patients diagnosed with early-stage BC, node-negative, and estrogen receptor-positive disease were identified from the Surveillance, Epidemiology, and End Results Oncotype DX database. Result We included 74,605 patients. Those with higher grade (p < 0.001) and progesterone receptor-negative (PR Neg) (p < 0.001) had the highest odds of a high-risk RS. Among them, 3.2%, 10.1%, 39.1%, 18.6%, 41.6%, and 80.1% had high-risk RS tumors in PR-positive (PR Pos)/well-differentiated (G1), PR Pos/moderately differentiated (G2), PR Pos/poorly and/or undifferentiated (G3), PR Neg/G1, PR Neg/G2, and PR Neg/G3 groups, respectively. Receipt of chemotherapy was associated with improved breast cancer-specific survival (p = 0.010) and overall survival (p < 0.001) in high-risk RS cohort. However, there were no survival benefits from chemotherapy in patients with PR Neg/G3 disease and other groups after stratification by grade and PR status (all p >= 0.05). Conclusion Our study aids in refining patient selection for the RS testing, which is crucial given its economic implications. However, 21-gene RS remains pivotal for treatment decision-making.