BACKGROUND & AIMS: To summarize the epidemiologic evidence and assess the validity of claimed associations of inflammatory bowel diseases (IBDs) with overall and site-specific cancer risk.

METHODS

We systematically searched PubMed, Embase, and Scopus from inception to May 10, 2021, to identify and comprehensively reanalyze the data of meta-analyses on associations between IBDs (ie, Crohn's disease [CD] and ulcerative colitis [UC]) and subsequent risk of cancer. The strength of epidemiologic evidence was graded as high, moderate, or weak, by applying prespecified criteria that included the random effects estimate, its 95% confidence interval, and P value, estimates of heterogeneity, small-study effects, and robustness to unmeasured confounding.

RESULTS

This study critically appraised 277 estimates derived from 24 published meta-analyses and our own meta-analyses. The association between pediatric-onset IBDs and overall risk of cancer showed high epidemiologic evidence. Twenty associations (15 cancer types) demonstrated moderate evidence: any cancer (pediatric-onset UC), mouth to terminal ileum (CD), small bowel (CD/UC), colon (CD), rectum (CD/UC), colon-rectum (IBDs, pediatric-onset CD/UC), bile ducts and liver (CD/UC), liver (CD), intrahepatic cholangiocarcinoma (IBDs), bile ducts (CD), skin (CD), squamous cell carcinoma of the skin (CD), nonmelanoma skin cancer (UC), kidney (CD), and thyroid cancer (IBDs). Another 40 associations (23 cancer types) showed statistical significance; however, our confidence in these effect estimates was weak. No statistical significance was found regarding further 47 associations.

CONCLUSIONS

Associations between IBDs and different types of malignancy showed varying levels of evidence and magnitude of risk. Further primary research investigating the impact of a consistent set of risk factors that are known to affect cancer risk is warranted.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO CRD42021254996.