A Matched Case-Control Analysis of Clinical Outcomes for Inflammatory Bowel Disease Patients with Rectal Cancer Treated with Pelvic Radiation Therapy.

Inflammatory bowel disease (IBD) is a known risk factor for rectal cancer, and radiation therapy (RT) is often an important part of therapy for these patients. Previously published studies have raised concerns for increased rates of RT toxicity in IBD patients. We performed a matched case-control analysis to assess RT-related toxicity in a large sample of US veterans afflicted with IBD and rectal cancer.We identified 186 veterans with rectal cancer (71 IBD patients treated with RT, 71 matched controls without IBD treated with RT, and 44 non-matched controls with IBD treated without RT) diagnosed between 2000 and 2015. We analyzed short and long-term toxicity as well as mortality in multivariable logistic regression, Fine-Gray, and frailty models, adjusting for potential confounders.When comparing IBD and non-IBD patients treated with RT there were no differences in RT breaks (adjusted odds ratio [aOR] 1.70 95% confidence interval [CI] 0.38-4.76, p=0.49) or the need for anti-diarrheal medication during RT (aOR 1.53, 95% CI 0.70-3.35, p=0.29). There was a trend toward higher risk of hospital admission during RT for RT + IBD patients (aOR 2.69, 95% CI 0.88-8.22, p=0.08). There were higher rates of small bowel obstruction (OR 15, 95% CI 1.9-115, p=0.009) and a trend toward higher rates of abdominopelvic adhesions (OR 3.6, 95% CI 0.98-13, p=0.05) in the RT + IBD cohort. However, when compared to a non-matched cohort of IBD patients treated without RT there were no differences in long-term complications. No differences were found in other acute or long-term toxicities. Rectal cancer-specific mortality appeared similar across all cohorts.Radiation therapy does not appear to increase the rates of acute or long-term toxicity in patients with IBD and should be considered a standard part of therapy when otherwise indicated.