Malignant melanoma of the anal region

Abstract

Malignant melanoma (MM) of the anal region is an uncommon disease. In many cases, the disease is undetected or mistaken for a benign polyp or haemorrhoids until it reaches an advanced state. Owing to delayed diagnosis and early metastases, the prognosis is often poor. In contrast to melanomas of the skin, a history of sun exposure does not seem to have an impact in development of MM in this region. Anorectal melanomas (AM) are most common in the rectum, followed by the anal canal and anal verge. Ras mutations, especially in codon 61 of the N-ras oncogene, are common in CM and rare in melanomas of the vulva and anorectum. The diagnosis of an AM is usually made using a biopsy. Histopathological examinations show spindle-shaped and pleomorphic cells. Adjuvant immunohistological markers are the calcium-binding protein S-100, the melanoma antigen HMB-45, the melanoma-expressed protein Melan A, and microphthalmia-associated transcription factor (MiTF). To date, there are few published guidelines for the correct management of AM, and surgery remains the mainstay of treatment. We report on a 39-year old man who presented with a 5-week history of recurrent prolapse of an anal tumour. The tumour was histologically confirmed to be malignant melanoma.