Impact of 21-Gene Recurrence Score on Chemotherapy Decision in Invasive Ductal Carcinoma of Breast with Nodal Micrometastases

PURPOSE: The purpose of this study was to investigate the effect of 21-gene recurrence score (RS) on predicting prognosis and chemotherapy decision in node micrometastases (N1mi) breast invasive ductal carcinoma (IDC). METHODS: Patients with stage T1-2N1mi and estrogen receptor-positive IDC diagnosed between 2004 and 2015 were included. The associations of 21-gene RS with breast cancer-specific survival (BCSS), chemotherapy decision, and benefit of chemotherapy were analyzed. RESULTS: We identified 4,758 patients including 1,403 patients (29.5%) treated with adjuvant chemotherapy. In the traditional RS cutoffs, 2,831 (59.5%), 1,634 (34.3%), and 293 (6.2%) patients were in the low-, intermediate-, and high-risk RS groups, respectively. In 3,853 patients with human epidermal growth factor receptor-2 (HER2) status available, most patients were HER2-negative disease (98.3%). A higher RS was independently related to chemotherapy receipt, and 14.0%, 47.7%, and 77.8% of patients in the low-, intermediate-, and high-risk RS groups received chemotherapy, respectively. The multivariate analysis indicated that a higher RS was related to worse BCSS (p < 0.001). The 5-year BCSS rates were 99.3%, 97.4%, and 91.9% in patients with low-, intermediate-, and high-risk RS groups, respectively (p < 0.001). However, chemotherapy receipt did not correlate with better BCSS in low-, intermediate-, or high-risk RS groups. There were similar trends using Trial Assigning Individualized Options for Treatment RS cutoffs. CONCLUSION: The 21-gene RS does predict outcome and impact on chemotherapy decision of N1mi breast IDC. Large cohort and long-term outcomes studies are needed to identify the effects of chemotherapy in N1mi patients by different 21-gene RS groups.