Amelanotic vulvar melanoma with intratumor histological heterogeneity.

Amelanotic vulvar melanoma is a rare type of malignant melanoma. This paper describes a case of an asymptomatic ulcerated nodule 20 mm in size. The tumor cells from the nodular lesion showed positive staining immunohistochemically for Melan-A, but negative staining with HMB-45. The cells showed negative reactivity to S-100 except in one region. The melanoma cells in the epidermis were detected in one of the specimens from the excised tumor nodule. The cells in the epidermis showed positive staining for Melan-A and S-100 and partial staining with HMB-45. The tumor was diagnosed as malignant melanoma of the vulva and immunohistochemically shown to have intratumor histological heterogeneity. This case suggests the importance of viewing non-pigmented nodules on the vulva of elderly females as potentially malignant melanoma, and that a combination of immunohistochemical stains may be useful for recognizing the stage of the melanosomes in the melanoma cells.