Background: Patients with longstanding inflammatory bowel disease are at high risk of developing intestinal cancers. In this study, we aimed to elucidate the differences between intestinal cancers associated with ulcerative colitis and Crohn’s disease. Methods: Intestinal cancers in ulcerative colitis and Crohn’s disease patients treated between 1983 and 2020 at 43 Japanese institutions were retrospectively analyzed. Results: A total of 1505 intestinal cancers in 1189 ulcerative colitis and 316 Crohn’s disease patients were studied. Almost all of ulcerative colitis-associated cancers (99%) were in the colon and rectum, whereas half of Crohn’s disease-associated cancers (44%) were in the anus, with 11% in the small intestine. Ulcerative colitis-associated cancers were diagnosed more frequently by surveillance (67% vs. 25%, P < 0.0001) and at earlier stages (stages 0–1, 71% vs. 27%, P < 0.0001) compared with Crohn’s disease-associated cancers. Colorectal cancers associated with Crohn’s disease showed a significantly worse 5-year overall survival rate than those associated with ulcerative colitis (stage 2, 76% vs. 89%, P = 0.01, stage 3, 18% vs. 68%, P = 0.0009, and stage 4, 0% vs. 13%, P = 0.04). Surveillance correlated with earlier diagnoses for ulcerative colitis- and Crohn’s disease-associated intestinal cancers, whereas shorter intervals between endoscopic examinations correlated with an earlier cancer diagnosis in ulcerative colitis patients but not in Crohn’s disease patients. Conclusions: The clinical and oncological features of ulcerative colitis- and Crohn’s disease-associated cancers were very different. Crohn’s disease-associated cancers were diagnosed at more advanced stages and were detected less frequently by surveillance. Additionally, they showed a significantly poorer prognosis.
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