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.