Mucinous cystadenocarcinoma of the appendix invading the ascending colon with fistula formation: report of a case.

Based on colonoscopy findings, we made a preoperative diagnosis of primary mucinous cystadenocarcinoma of the appendix with features of a submucosal tumor (SMT) in the ascending colon. A 59-year-old woman who presented with right lower quadrant abdominal pain underwent colonoscopy, which revealed an SMT with three nodules covered with mucus in the ascending colon. Examination of colonoscopic biopsy specimens indicated "very" well-differentiated adenocarcinoma with mucus lakes. Abdominal computed tomography showed irregular wall thickness from the cecum to the ascending colon. The adjacent appendix had an enhanced wall and unclear border against the ascending colon. Thus, we performed right hemicolectomy, with good results. Histopathological examination revealed mucinous cystadenocarcinoma of the appendix, invading the ascending colon with fistula formation. Appendiceal tumors can manifest with a variety of colonoscopic features, and curative surgical resection should be attempted even if there is fistula formation.