Anal carcinoma in inflammatory bowel disease

We followed 9602 patients with Crohn's disease or ulcerative colitis for anal squamous cell carcinoma for up to 18 years. No significant increase was observed: two cases occurred vs 1.3 expected during 99,229 person-years of observation, (standardized incidence ratio = 1.6; 95 confidence interval: 0.2-5.7). Anal squamous cell carcinoma is rare even in inflammatory bowel disease.