Rectal malignant melanoma diagnosed by N-isopropyl- p-123I-iodoamphetamine single photon emission computed tomography and 5-S-cysteinyl dopa: report of a case.

Malignant melanoma in the anorectal region is a rare disease associated with a very poor prognosis. Taking a biopsy of malignant melanoma is generally contraindicated because of the high risk of inducing metastasis. Although clinical examination and imaging findings are important for the preoperative diagnosis, conventional imaging techniques sometimes fail to provide information from which an accurate diagnosis can be made. We recently treated an 84-year-old woman with rectal malignant melanoma, in whom magnetic resonance imaging showed atypical findings. On the other hand, N-isopropyl- p-(123)I-iodoamphetamine single photon emission computed tomography and 5- S-cysteinyl dopa in blood serum, as a tumor marker of malignant melanoma, proved very effective for establishing the preoperative diagnosis. Despite radical abdominoperineal resection, the patient died of multiple liver and lung metastases about 5 months after surgery.