Clinicopathologic Presentation and Natural History of Anorectal Melanoma: A Case Series of 18 Patients.

Anorectal melanoma is a rare malignant neoplasm with variable natural history and nonspecific presentation. We describe the clinicopathologic and prognostic parameters of a series of 18 patients (16 [88.9%] white; 10 [55.6%] male; median age, 64.0 years [interquartile range, 45.8-74.3 years]) with histologically proven anorectal melanoma treated at our institution during a 21-year period between October 1991 and August 2012. Late diagnosis was common (44.5% of patients had stage II disease or worse at diagnosis), likely owing to a delay in presentation, nonspecific presenting symptoms, and frequent incorrect diagnoses (16 cases [88.9%]). Overall disease-specific mortality was 66.7% (12 of 18 patients), with a median time to death of 15.5 months (interquartile range, 7.3-25.5 months). Disease-specific survival was significantly better following wide local excision vs abdominoperineal resection (P = .04), although patients undergoing the former tended to have fewer rectal lesions (P = .04), smaller lesions (P = .02), and a trend toward less advanced stage (P = .06). Larger studies assessing optimal medical and surgical management for anorectal melanoma are needed to improve outcomes.