Primary rectal malignant melanoma: a rare case report

Primary malignant melanoma of the rectum is a rare and highly aggressive malignant tumor. Its clinical manifestations lack specificity and it is often misdiagnosed as hemorrhoids or rectal polyps, with a very poor prognosis. This article reported a case of a 71-year-old Asian female who presented with changes in bowel habits and hematochezia. Colonoscopic biopsy and immunohistochemistry confirmed the diagnosis of primary malignant melanoma of the rectum, with no primary lesions found on the skin. Imaging suggested a lesion in the lower rectum, and postoperative pathology and immunohistochemistry showed positivity for Melan A, HMB45, and SOX10, with a Ki-67 proliferation index of approximately 45%, consistent with characteristics of malignant melanoma. The patient underwent robot-assisted laparoscopic abdominoperineal resection (Miles operation) and did not receive postoperative immunotherapy; during a 6-month follow-up, no recurrence or metastasis was observed. Literature review indicates that the diagnosis of rectal malignant melanoma relies on immunohistochemistry, the choice of surgical approach remains controversial, and immune checkpoint inhibitors have shown good efficacy in advanced patients. This case highlights the need to raise clinical awareness of this disease to achieve early diagnosis and individualized treatment selection, which may improve patient prognosis.