Risk of colorectal cancer by family history of both colorectal carcinomas and colorectal polyps: a nationwide cohort study.

Background: The increased risk of colorectal cancer (CRC) associated with family history of both colorectal in situ or invasive carcinomas (Stage 0 to IV) and colorectal polyps is attributed solely to family history of CRC, resulting in an underestimation of the actual risk. We aimed to assess the association between overall and early-onset CRC (EOCRC) risk and family history of both colorectal carcinomas and polyps.

Methods: We conducted a nationwide cohort study leveraging Swedish family-cancer datasets with follow-up from 1964 to 2018. Standardized incidence ratios (SIRs) were calculated to estimate the risk of CRC and EOCRC among individuals with a family history of both colorectal polyps and carcinomas.

Results: We followed up 13,432,205 individuals for up to 54 years. The risk of overall CRC was 2.2 times increased in individuals with 1 first-degree relative (FDR) with one-time polyp diagnosis and an additional FDR with carcinoma (95% CI = 2.1-2.3; EOCRC SIR = 2.9 [95% CI = 2.4-3.4]). The risk was significantly higher in individuals with 1 FDR with repeated polyp diagnoses (≥2 times) and an additional FDR with carcinoma (overall SIR = 2.9 [95% CI = 2.7-3.1]; EOCRC SIR = 5.4 [95% CI = 3.9-6.4]). A similar risk was observed in individuals with ≥2 FDRs with one-time polyp diagnosis and an additional FDR with carcinoma (overall SIR = 2.9 [95% CI = 2.4-3.4]; EOCRC SIR = 5.3 [95% CI = 3.0-8.6]). Individuals with ≥2 FDRs with repeated polyp diagnoses and an additional FDR with carcinoma had a 5.0-fold overall risk (95% CI = 4.3-5.7) and a 13.8-fold EOCRC risk (95% CI = 9.7-20.1). Younger age at polyp/carcinoma diagnoses, and more relatives with polyps and carcinomas were associated with higher CRC risk.

Conclusions: Individuals with a family history of both colorectal polyps and carcinomas are at significantly increased risk of CRC, especially EOCRC. The risk increased with frequent polyp diagnoses, younger age at first polyp/carcinoma diagnoses, and the number of relatives with polyps/carcinomas. This study highlights the importance of considering both colorectal polyps and carcinomas in family history when assessing CRC risk. These findings could supplement current screening guidelines.