Background: Previous reports suggest that relatives of colorectal cancer (CRC)-affected probands carrying the BRAF p.V600E mutation are at an increased risk of CRC and extracolonic cancers (ECC). In this study, we estimated the association between a family history of either CRC or ECC and risk of CRC with a BRAF p.V600E mutation. Methods: Population-based CRC cases (probands, ages 18-59 years at diagnosis), recruited irrespective of family cancer history, were characterized for BRAF p.V600E mutation and mismatch repair (MMR) status. ORs and 95% confidence intervals (CI) were estimated using multivariable logistic regression. Results: The 690 eligible probands showed a mean age at CRC diagnosis of 46.9+7.8 years, with 313 (47.9%) reporting a family history of CRC and 53 (7.7%) that were BRAF-mutated. Probands with BRAF-mutated, MMR-proficient CRCswere less likely to have a family history ofCRCthan probands that wereBRAFwild-type (OR, 0.46; 95% CI, 0.24-0.91; P=0.03). For probands with a BRAF-mutated CRC, the mean age at diagnosis was greater for those with a CRC-affected first- or second-degree relative (49.3 + 6.4 years) compared with those without a family history (43.8 + 10.2 years; P = 0.04). The older the age at diagnosis of CRC with the BRAF p. V600E mutation, the more likely these probands were to show a family history of CRC (OR, 1.09 per year of age; 95% CI, 1.00-1.18; P = 0.04). Conclusions: Probands with early-onset,BRAF-mutated, andMMR-proficientCRCwere less likely to have a family history of CRC than probands that were BRAF-wild-type. Impact: These findings provide useful insights for cancer risk assessment in families and suggest that familial or inherited factors are more important in early-onset, BRAF-wild-type CRC. Cancer Epidemiol Biomarkers Prev; 22(5); 917-26.
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