The association between cancer treatments and exacerbation of IBD is unclear. We aimed to evaluate the effects of cancer treatments on the disease activity of IBD.
We performed a systematic review of the literature on cancer therapy in patients with pre-existing IBD. Electronic searches of PubMed, Cochrane Library, and Embase were combined with manual searches (September 2021). Meta-analysis was performed using the random-effects model. The primary outcome was flares of IBD following cancer therapy. Secondary outcomes were need for IBD-related hospitalization, surgery, and initiation or intensification of steroid or biological treatments to manage IBD flares.
In total, 33 studies were included in the systematic review, comprising 1,298 patients with IBD who received cancer treatment. The overall occurrence of IBD flares following cancer treatment was 30% (95% confidence interval (CI) 23-37%). IBD flares resulted in utilization of systemic steroids and biologic therapies among 25% and 10%, respectively, and in discontinuation of cancer treatment among 14% of patients. Finally, risk of gastrointestinal toxicity following immune check point inhibitor treatment (ICI) was increased in patients with IBD compared to patients without IBD (RR=3.62 (95%CI 2.57-5.09). Despite this, the studies generally reported that flares were manageable.
Current data indicate a high proportion of patients with IBD experiencing a flare following the start of cancer treatment. Patients with IBD were at increased risk of gastrointestinal toxicity following ICI treatment compared to those without IBD. However, cancer therapy-induced IBD flares were manageable and should not preclude appropriate cancer treatments.

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