e23084 Background: The association between cancer treatments and impact of inflammatory bowel diseases (IBD) remains uncertain. Given the growing prevalence of IBD globally, it is crucial to understand the impact of various cancer treatments in this patient population to make informed decisions and optimize outcomes. Thus, the objective of our systematic review is to assess how cancer treatments impact the activity of underlying IBD. Methods: We performed a systematic review of the literature on cancer therapy in patients with pre-existing IBD. Various databases like PubMed, Cochrane, Embase and Google Scholar were searched for studies reporting effects of cancer treatment in patients with IBD, till February 1, 2024. Studies without relevant data were excluded. The outcomes studied were the flares of IBD following cancer treatment and initiation of systemic steroids or biologics for management of IBD flares. Results: In total, 36 studies were included which comprised 1,443 patients with IBD who received cancer treatment. The overall occurrence of IBD flares in patients with IBD receiving cancer treatment was 28% (CI 22.9%-33.8%, I2= 68%) out of which 35.9% (CI 27.5% - 45.3%, I2= 40) had received immune checkpoint inhibitor therapy. The flares resulted in the utilization of systemic steroids and biologics in 27% and 10% respectively. Conclusions: While the data suggests a high proportion of patients with IBD experience flares during cancer treatment, all of the reported episodes were manageable with steroids and/or biologics. However, the population studied only included 1443 patients, and larger population studies are required to optimize individual outcomes, and to explore methods to minimize severity and frequency of flares, when possible.