Associations of Inflammatory Bowel Disease and Subsequent Cancers in a Population-Based Study of Older Adults in the United States

Background: Cancer risk is elevated in patients with inflammatory bowel disease (IBD). A comprehensive investigation of cancer risk in older patients (≥66 years of age) is needed, because this understudied population is at high risk. Methods: We performed a case-control study using Surveillance Epidemiology and End Results-Medicare data including 1,986-735 incident cancer cases (aged 66-99 years; diagnosed 1992-2015) and 200,000 controls matched by sex, age, race and ethnicity, and selection year. IBD was identified by ulcerative colitis (UC) or Crohn's disease (CD) diagnosis codes. Odds ratios (ORs) and 95% confidence intervals (CIs) were estimated with logistic regression, adjusting for potential confounders. For colorectal cancers, we further adjusted for screening rates. We assessed confounding by medication exposure among patients with prescription drug coverage. Results: IBD, CD, and UC were present in 0.8%, 0.3%, and 0.5% in both cancer cases and non-cancer controls. Of 51 cancers examined, IBD was statistically significantly associated with cancers of the small intestine (OR = 2.55, 95% CI = 2.15 to 3.01), intrahepatic (OR = 1.92, 95% CI = 1.47 to 2.51) and extrahepatic bile ducts (OR = 1.75, 95% CI = 1.38 to 2.22), rectum (OR = 1.61, 95% CI = 1.36 to 1.90), and colon (OR = 1.21, 95% CI = 1.10 to 1.33). CD was associated with cancers of the small intestine (OR = 4.55, 95% CI = 3.65 to 5.67), and UC was associated with cancers of the intrahepatic bile ducts (OR = 1.87, 95% CI = 1.34 to 2.61), rectum (OR = 1.80, 95% CI = 1.47 to 2.20), and colon (OR = 1.28, 95% CI = 1.14 to 1.43). After adjusting for medication exposure, IBD was not statistically significantly associated with lung cancer, melanoma, diffuse large B-cell lymphoma, and myelodysplastic syndrome. Conclusions: In this large study among older adults (≥66 years of age), IBD was positively associated with gastrointestinal cancers. Associations with extraintestinal cancers may reflect the effect of immunosuppressive medications.