Risks of colorectal and extracolonic cancers following colorectal cancer: a systematic review and meta-analysis.

Background: Colorectal cancer survivors face increased risks of developing new primary cancers in colorectum and other anatomical sites. This systematic review aimed to estimate primary colorectal and extracolonic cancers risks following colorectal cancer.

Methods: Peer-reviewed articles published before January 2025 were screened across 4 databases to identify studies using population cancer registry reporting standardized incidence ratios (SIRs) of primary cancers following colorectal cancer, compared with the general population. A meta-analysis was conducted to summarize the SIRs, and age-specific cumulative risks of primary cancers following colorectal cancer were estimated using the summarized SIRs and age-, sex-, calendar-, region-, and cancer-specific incidence data.

Results: Of 8254 articles identified, 57 were included in meta-analysis. The pooled SIRs (95% confidence interval) for any primary cancer, extracolonic cancer and colorectal cancer were 1.13 (1.06 to 1.20), 1.10 (1.03 to 1.17), and 1.55 (1.33 to 1.77), respectively. Increased risks were also observed for primary cancers of small intestine, ovary, uterus, testes, kidney, female breast, thyroid, and prostate overall, as well as for lung and urinary bladder cancer in recent studies. The cumulative risks of any primary cancer, extracolonic cancer, and colorectal cancer to age 75 years were 38.5%, 31.6%, and 8.24% in Australasia; 33.8%, 30.9%, and 4.77% in North America; 27.4%, 25.6%, and 8.01% in East Asia; and 33.4%, 28.8%, and 4.68% in Europe.

Conclusion: Colorectal cancer survivors have an increased risk of subsequent primary cancers, both extracolonic and colorectal, when compared with the general population. These findings underscore the necessity for tailored surveillance and prevention strategies to effectively identify and manage subsequent primary cancers in this population.