Abstract
A 44-year-old man presented with melena and having an anal fistula associated with a 5 × 3 cm peri-anal tumor with a history of peri-anal abscess drainage three times previously. Sigmoid colon cancer was found in the colonoscopy and he was transferred to our hospital. After sigmoidectomy with lymph node dissection and local resection for the anal fistula with tumor, the sigmoid cancer was classified as stage IIIb. Histologically, both the sigmoid and anal tumors showed two virtually-identical, moderately-differentiated adenocarcinomas. We surmise that malignant sigmoid colon cells were implanted within the anal fistula, developing a metastatic focus. After systemic adjuvant chemotherapy and radiation for the anal lesion, no recurrence has been seen in 4 years 9 months of follow-up. Colorectal cancer implantation in an anal fistula is rare, so far as we know, with just 33 cases including Japanese cases reports, recorded since 1954. It should be not forgotten, however, that this is a potential complication of primary malignancy since metastatic cancer occurs in chronic/recurrent anal abscesses and peri-anal fistula.
