A rare case of rectal cancer with perianal metastasis: a case report

BACKGROUND: Cancer metastasis from colon cancer to an anal fistula is very rare. We herein reported a rare case in which local excision was performed for metastatic anal fistula cancer originating from rectal cancer. CASE PRESENTATION: A 68-year-old man was referred to our institution with a diagnosis of rectal cancer. He had complained of anal fistula for 5 years. Based on a recent history of cerebral infarction, Hartmann’s operation was performed to treat the rectal cancer after the administration of preoperative chemotherapy for 3 months. However, 1 month after Hartmann’s operation, the anal fistula was found to have worsened. Pelvic magnetic resonance imaging (MRI) revealed tumor formation at the perianal lesion. Metastatic anal fistula cancer originating from the rectal cancer was diagnosed based on the examination of the biopsied tissue. We selected local excision because the anal tumor had not invaded the surrounding tissue. There has been no recurrence in the 31 months after the curative operation. CONCLUSION: Metastatic cancer should be ruled out when treating left-sided colon cancer with anal fistula. Local excision is one possible treatment for metastatic anal fistula cancer.