Second primary cancers after sporadic and familial colorectal cancer.

Second cancers were studied among 68,104 cases of colorectal cancer (CRC) from the Swedish Family-Cancer Database. A total of 1,113 patients received a diagnosis of second CRC; 25 of them had a family history of CRC. Cases of second CRC with a family history were diagnosed up to 10 years before sporadic cases. The relative risk (RR) of all second CRCs was 2.21 compared with the first CRC. Familial second CRCs had a 2-fold risk compared with the sporadic forms. Age of onset was the most important covariate of second CRCs; the relative risk at ages 15-39 years was 27 compared with the first CRC. Familial CRC was associated with a high risk of small-intestinal, endometrial, and gastric cancers apart from CRC, all typical of hereditary nonpolyposis CRC (HNPCC). Among familial cases, 36% of second CRCs and 100% of endometrial cancers came from families that fulfilled the Bethesda criteria for HNPCC. Only 12 families conformed to the Amsterdam criteria; in family members, the risk of second CRC was 127-fold and that of endometrial cancer 257-fold. Other sites that were in excess among all second cancers were many cancers linked to HNPCC and, additionally, breast, prostate, thyroid and other endocrine, skin, and genital cancers. The high risk of second cancer after early-onset CRC calls for evaluation of family history and clinical surveillance.