BRCA1 function is inactivated through BRCA1 promoter methylation in a substantial number of triple-negative breast cancers. We investigated the impact of BRCA1-methylation status on the efficacy of adjuvant chemotherapy in patients with triple-negative breast cancer or with non-triple-negative breast cancer.

BRCA1 promoter methylation was assessed in 1163 unselected breast cancer patients. Methylation was evaluated using a methylation-specific PCR (MSP) assay.

In the subgroup of 167 triple-negative breast cancer patients who received adjuvant chemotherapy, patients with BRCA1-methylated tumors had a superior 10-year disease-free survival (DFS)(78% versus 55%, P = 0.009) and 10-year disease-specific survival (DSS) (85% versus 69%, P = 0.024) than those with BRCA1-unmethylated tumors, and BRCA1 methylation was an independent favorable predictor of DFS and DSS in a multivariate analysis in this subgroup [DFS: hazard ratio (HR) = 0.45; 95% confidence interval (CI) 0.24–0.84; P = 0.019; DSS: HR = 0.43; 95% CI = 0.19–0.95; P = 0.044]. In contrast, in 675 non-triple-negative breast cancer patients who received adjuvant chemotherapy, BRCA1 methylation was an unfavorable predictor of DFS and DSS in univariate analysis (DFS: HR = 1.56; 95% CI 1.16–2.12; P = 0.003; DSS: HR = 1.53; 95% CI = 1.05–2.21; P = 0.026).

Triple-negative breast cancer patients with BRCA1-methylated tumors are sensitive to adjuvant chemotherapy and have a favorable survival compared with patients with BRCA1-unmethylated triple-negative tumors.