A case of anastomotic recurrence 12 years after intersphincteric resection for anorectal malignant melanoma

Anorectal malignant melanoma (AMM) is a rare disease with a poor prognosis, accounting for < 1.0% of all malignant melanomas and a 5-year survival rate of 19.2%. The treatment is mainly surgical, and lymph-node dissection is often performed. Cases of recurrence after a prolonged period (> 10 years), as in the present case, are rare. The patient was an 80-year-old woman who underwent laparoscopic intersphincteric resection with bilateral lateral lymph-node dissection for the diagnosis of primary AMM of the lower rectum at X - 12 years. The pathology was pStage III and the resection margins were negative. Twelve years after the initial surgery, in year X, the patient visited our hospital with the chief complaint of discomfort due to a tumor in the anorectal region. Biopsy revealed a recurrence, and laparoscopic abdominoperineal resection was performed. Based on the pathological findings, the patient was diagnosed with local recurrence of the anastomotic anal canal. Both the first and second specimens were negative for BRAF V600E/K mutation. Four months have passed since the surgery, and the patient continued to receive nivolumab without recurrence. Long-term local follow-up is necessary when the anal canal is preserved during AMM surgery.