Anal malignant melanoma and soft-tissue malignant fibrous histiocytoma in neurofibromatosis type 1.

A 48-year-old man with the nonfamilial form of neurofibromatosis type 1 (NF-1) developed a malignant fibrous histiocytoma in the deep soft tissue of the calf. Following excision and local radiotherapy, the tumor did not recur. At age 59, due to rectal bleeding, a polypoid malignant melanoma of the anal canal was detected and resected. One year later a local recurrence was removed, a pelvic mass was seen on computed tomography, and the patient died. The malignant melanoma was amelanotic and negative for HMB-45 (a melanoma-specific antibody), and the recurrent tumor showed areas of desmoplasia and prominent perineural and intraneural spread. The latter properties underscore the similarities of this melanoma to malignant peripheral nerve sheath tumor. In addition to neurofibroma and malignant schwannoma, NF-1 is associated with other neuroectodermal tumors, including brain tumors and pheochromocytoma. However, it is still controversial whether cutaneous malignant melanoma is more prevalent in NF-1 patients. Anorectal melanoma and malignant fibrous histiocytoma are exceedingly rare in NF-1. Second primary cancers are probably more frequent in NF-1 patients compared to the general population and may be related to alterations in the NF-1 gene.