Invasive ductal adenocarcinoma arising from pancreatic heterotopia in rectum: case report and review of literature.

Pancreatic heterotopia has been described at several abdominal and intrathoracic locations, most commonly in the stomach and upper part of the small intestine. Its occurrence in the rectum is unusual, and malignant transformation in the rectum has not been reported. We report a case of ductal adenocarcinoma arising in a rectal pancreatic heterotopia in a 42-year-old woman with delayed local recurrence. The tumor was composed of well to moderately differentiated ductal adenocarcinoma infiltrating through the full thickness of the anorectal wall with extension into the vaginal septum. A focus of ectopic pancreas consisting of exocrine acini and small ducts adjacent to the tumor with some ducts showing mild to severe dysplasia reminiscent of pancreatic intraepithelial neoplasia was also observed. Although our literature search found 31 documented reports of tumors arising in the heterotopic pancreas, the present case is the first case of ductal adenocarcinoma arising in a focus of pancreatic heterotopia in the rectum.