Implantation metastasis of rectosigmoid cancer in an anal fistula

Implantation metastasis of colorectal cancer in an anal fistula is very rare. We report a case of a 61 years old male who underwent fistulectomy for an anal fistula. Histopathology unexpectedly revealed adenocarcinoma in the fistula track, however the patient refused further treatment. Sixteen months later he presented with an obstructing locally advanced rectosigmoid cancer found to be fixed into the pelvic wall. An ileosigmoid bypass was fashioned and he was treated with neoadjuvant chemoradiotherapy followed by high anterior resection. Histopathology confirmed a colorectal adenocarcinoma, Immunohistochemistry of the tumors from both sites was CK7-/CK20+. The patient died 34 months later with liver and lung metastasis however no perianal recurrence occurred. Local resection with or without radiotherapy, instead of abdominoperineal resection, was feasible for control of perianal metastatic lesion implanted from colorectal cancer if local extended resection was possible.