To Örebro University

Background and Aims: The association between microscopic colitis [MC] and cancer risk is unclear. Large, population-based studies are lacking.

Methods: We conducted a nationwide cohort study of 11 758 patients with incident MC [diagnosed 1990-2016 in Sweden], 50 828 matched reference individuals, and 11 614 siblings to MC patients. Data were obtained through Sweden's pathology departments and from the Swedish Cancer Register. Adjusted hazard ratios [aHRs] were calculated using Cox proportional hazards models.

Results: At the end of follow-up [mean: 6.7 years], 1239 [10.5%] of MC patients had received a cancer diagnosis, compared with 4815 [9.5%] of reference individuals (aHR 1.08 [95% confidence interval1.02-1.16]). The risk of cancer was highest during the first year of follow up. The absolute excess risks for cancer at 5, 10, and 20 years after MC diagnosis were + 1.0% (95% confidence interval [C1]0.4%-1.6%), +1.5% [0.4%-2.6%], and + 3.7% [-2.3-9.6%], respectively, equivalent to one extra cancer event in every 55 individuals with MC followed for 10 years. MC was associated with an increased risk of lymphoma (aHR 1.43 [1.06-1.92]) and lung cancer (aHR 1.32 [1.04-1.68]) but with decreased risks of colorectal (aHR 0.52 [0.40-0.66]) and gastrointestinal cancers (aHR 0.72 [0.60-0.85]). We found no association with breast or bladder cancer. Using siblings as reference group to minimise the impact of shared genetic and early environmental factors, patients with MC were still at an increased risk of cancer (HR 1.20 [1.06-1.36]).

Conclusions: This nationwide cohort study demonstrated an 8% increased risk of cancer in MC patients. The risk was highest during the first year of follow-up.