Abstract
PURPOSE: To investigate the effect of 21-gene recurrence score (RS) on chemotherapy-decision making and prognosis in breast cancer patients aged <40 years. METHODS: Using the Surveillance, Epidemiology, and End Results program, we included patients aged <40 years with tumor size ≤5 cm, node negative, and estrogen receptor-positive breast cancer between 2004 and 2015. Correlations among the 21-gene RS, chemotherapy decision-making and prognosis were analyzed. RESULTS: We included 2721 patients in this study. According to TAILORx cutoffs, 352 (12.9%), 1814 (66.7%), and 555 (20.4%) patients were classified as low-, intermediate-, and high-risk cohorts, respectively. The 21-gene RS categories were associated with the probability of receiving chemotherapy, with 7.1%, 33.4%, and 77.1% of patients in low-, intermediate-, and high-risk cohorts treated with chemotherapy, respectively (P < 0.001). Those in the intermediate-risk cohort were significantly less likely to receive chemotherapy over time (P = 0.008), and the trends of chemotherapy receipt were stable in the low-risk and high-risk cohorts over time. Multivariate analysis showed that the 21-gene RS was an independent prognostic indicator for breast cancer specific survival. In the stratified analysis, the receipt of chemotherapy was associated with better breast cancer specific survival in the high-risk cohort (P = 0.028), but not in the intermediate-risk cohort (P = 0.223). CONCLUSIONS: 21-gene RS has clinical implications for young breast cancer patients with respect to optimizing chemotherapy-decisions. Despite increasing rates of chemotherapy receipt in young patients, more studies are needed to determine the definitive effect of chemotherapy in young patients with three RS categories.