Contralateral breast cancer risk in BRCA1 and BRCA2 mutation carriers in a large cohort of unselected Chinese breast cancer patients

To estimate the cumulative risk of contralateral breast cancer (CBC) in BRCA1/2 carriers in a large cohort of unselected Chinese breast cancer patients. Our study comprised 9,401 unselected Chinese breast cancer patients and BRCA1/2 germline mutations were determined in all patients. After a median follow‐up of 5.7 years, 181 patients developed CBC in this cohort. Compared to noncarriers, BRCA1 and BRCA2 carriers had a 4.52‐fold (95% CI, 2.63–7.76) and 5.54‐fold (95% CI, 3.51–8.74) increased risk of CBC, respectively. The 10‐year cumulative risk of CBC was 15.5% (95% CI, 9.9–24.2) for BRCA1 carriers, 17.5% (95% CI, 10.9–28.0) for BRCA2 carriers and 3.2% (95% CI, 2.5–4.1) for noncarriers. Younger age at first breast cancer diagnosis was significantly associated with an increased 10‐year risk of CBC for BRCA1 carriers (≤40 years vs . >40 years: 21.5% vs . 11.9%, unadjusted hazard ratio [HR] = 2.51, 95% CI, 1.03–6.15, p = 0.044), but not for BRCA2 carriers and noncarriers. The 10‐year cumulative CBC risk was significantly higher in both BRCA1 and BRCA2 carriers who had a family history of breast cancer than in those who did not ( BRCA1 : 27.5% vs . 9.4%, adjusted HR = 2.64, 95% CI, 1.01–6.97, p = 0.049; BRCA2 : 27.1% vs . 12.8%, adjusted HR = 2.29, 95% CI, 1.04–5.06, p = 0.040). In conclusion, the risk of CBC was a substantial high in BRCA1/2 carriers in unselected Chinese breast cancer patients, and CBC risk is much more remarkable in both BRCA1 and BRCA2 carriers who had a family history of breast cancer. Younger age at first breast cancer diagnosis also enhanced CBC risk in BRCA1 carriers.