Allelic loss of the NF1 gene in anal malignant melanoma in a patient with neurofibromatosis type 1.

A 64-year-old man with neurofibromatosis type 1 (NF1) developed a primary malignant melanoma of the anus. Genetic analysis of the resected tumor confirmed loss of heterozygosity (LOH) of the NF1 gene. Anorectal malignant melanoma in NF1 is extremely rare, and genetic studies of the NF1 gene in such patients have not been reported. The allelic loss detected in the present patient supports the previously raised idea that NF1 can function as a tumor suppressor gene in the development of malignant melanoma in patients with NF1.