Familial adenomatous polyposis: a case report and histologic mucin study.

Adenocarcinoma arising at an ileostomy is uncommon, and only 29 cases have been reported in the literature. The case of a 54-year-old man who developed an adenocarcinoma at a Brooke ileostomy is reported. The ileostomy had been fashioned 21 years earlier after proctocolectomy for familial adenomatous polyposis (FAP). A wide local excision of the stoma was performed, and a new Brooke ileostomy was fashioned on the opposite side of the abdomen. Histopathologic examination revealed a well-differentiated adenocarcinoma with early invasion of the submucosa. On hematoxylin and eosin staining, the ileal mucosa adjacent to the tumor showed signs of colonic metaplasia, including loss of villous architecture and a reduced number of Paneth cells. Mucin staining using the high iron diamine-alcian blue stain demonstrated a mixture of sulfomucin and sialomucin in the ileal mucosa near the tumor, confirming colonic metaplasia. Ileostomy site carcinogenesis can be attributed to both the colonic metaplasia and the inherent nature of FAP or ulcerative colitis (UC), where colonic mucosa is susceptible to adenoma formation or dysplasia. Longstanding ileostomies in patients with FAP or UC should be followed to exclude the development of adenoma, dysplasia, or cancer.