Rectosigmoid adenocarcinoma revealed by metastatic anal fistula. The visible part of the iceberg: a report of two cases with literature review.

Colonic adenocarcinoma revealed by metastatic anorectal fistula is rare, with few cases in the literature. Such lesions can be taken for the more common manifestation of a benign perianal abscess or fistula. Once diagnosed, the management of such conditions remains controversial. We herein report two cases with perianal fistula that were subsequently found to have developed perianal adenocarcinoma on biopsy. Further colonic investigation revealed a rectosigmoid adenocarcinoma. Histology and immunohistochemical staining was identical in both primary and metastatic tumors. Preoperative chemoradiation with further rectal low anterior resection and local excision of metastatic anal fistula was performed. There is no recurrence after 3 years of follow-up.