Transanal sphincter-sparing local excision for primary anorectal malignant melanoma: a case report

Background: Anorectal malignant melanoma (ARMM) is a rare and highly aggressive malignancy with a poor prognosis. Surgical resection remains the primary treatment strategy, with local excision (LE) and extended resection (ER) being the most commonly performed approaches. However, the optimal surgical management remains controversial, particularly regarding oncologic control and sphincter preservation. Case presentation: We report a 61-year-old man who presented with painless hematochezia for one month. Imaging revealed a 4 × 4 cm mass near the dentate line, and colonoscopic biopsy confirmed malignant melanoma. After multidisciplinary evaluation, transanal sphincter-preserving local excision was performed under combined spinal-epidural anesthesia. The tumor was resected with preservation of anal function, and the postoperative course was uneventful without fecal incontinence. However, the patient died 14 months after surgery. Conclusion: This case illustrates that transanal sphincter-sparing local excision may be a feasible surgical option for carefully selected patients with localized primary anorectal malignant melanoma without sphincter involvement or distant metastasis. Nevertheless, longer follow-up and further studies are required to evaluate long-term oncologic outcomes.