Abstract
Malignant melanomas, which are rarely found in the Asian population, are malignant tumors or melanocytes that manifest in the skin mucosa. Malignant melanomas of the anorectum are very rare and account for approximately 1% of all malignant melanomas in the Asian population. Here, we present a rare case presenting a malignant melanoma of the anorectum. An 85-year-old woman visited the hospital with bloody stools and an anal mass. Sigmoidoscopy revealed a black mass protruding from the anus, and the scope was able to penetrate the anorectal mass. Close-up endoscopy revealed black moles of different sizes scattered across the rectal mucosa. PET-CT indicated multiple FDG uptakes in the liver, indicating multiple metastases. Pathologic examination led to the detection of malignant melanocytes with dark brown deposits. The patient's immunohistochemical markers were positive for melanin-A antibodies and HMB-45, indicating a malignant melanoma. As there was no evidence of malignant melanomas on the skin, the patient was diagnosed with primary malignant anorectal melanoma with liver metastases.
