Incidence of colorectal cancer in BRCA1 and BRCA2 mutation carriers: results from a follow-up study

Background:The BRCA1 and BRCA2 genes confer increased susceptibility to breast and ovarian cancer and to a spectrum of other cancers. There is controversy regarding the risk of colorectal cancer conferred by germline mutations in these two genes.Methods:We followed 7015 women with a BRCA mutation for new cases of colorectal cancer. Incidence rates in carriers were compared with population-specific incidence rates, and standardised incidence ratios (SIRs) were estimated. The expected numbers of cancers were computed by multiplying person–years at risk by the appropriate age-, sex- and country-specific incidence rates from the five countries.Results:Twenty-one incident colorectal cancer cases were observed among all mutation carriers, compared with 23.6 cases expected. The SIR for BRCA1 carriers was 0.92 (95% confidence interval (CI), 0.54–1.40, P=0.7) and for BRCA2 carriers was 0.82 (95% CI, 0.30–1.81, P=0.7). The SIR for colon cancer was 3.81 (95% CI 1.77–7.23) for women below the age of 50 years (both genes combined) and was 0.60 (95% CI 0.33–1.00) for women aged 50 years and above.Conclusion:The risk of colorectal cancer is increased in female carriers of BRCA1 mutations below the age of 50 years but not in women with BRCA2 mutations or in older women.