Anorectal Melanoma

Excerpt

Anorectal melanoma (AM) is a rare malignancy, characterized by aggressive behavior and a poor prognosis. AM is more frequent in female patients aged over 50 years. AM accounts for 0.4–1.6% of all melanomas, 23.8% of all mucosal melanomas, and 1% of all anorectal malignant tumors. There are many theories regarding AM pathogenesis. Some consider that AM may be related to oxidative stress in the region and/or to immunosuppression. Others propose that AM may derive from Schwannian neuroblastic cells or cells of the amine-precursor uptake and decarboxylation system of the gut. Assessment of pigmented lesions located on hidden areas is difficult. Together with late and nonspecific signs and symptoms which usually occur only in conjunction with large masses, diagnosis of these mucosal melanomas is often delayed. Most frequently, the signs and symptoms are obstruction, rectal bleeding, pain, or rectal tenesmus. There are various histological variants of AM: epithelioid, spindle cell, lymphoma-like, and pleomorphic. Surgery (abdominoperineal resection or local excision) is the most effective treatment for AM; however, this is not associated with improved overall survival. Recurrence is more frequent in cases of anorectal and rectal involvement when compared with anal-only involvement. There is currently no consensus about the most appropriate systemic treatment. The efficacy of some protocols previously used in patients with cutaneous melanomas is currently being studied in mucosal melanoma.