Use of antibodies to intermediate filaments in the diagnosis of metastatic amelanotic malignant melanoma.

Immunofluorescent staining of tissue from a lung tumor detected 12 years after excision of a primary malignant melanoma of the skin was negative for prekeratin and positive for vimentin, indicating that the tumor was not epithelial in origin and excluding carcinoma from the differential diagnosis. Complementary conventional staining with hematoxylin-eosin confirmed the melanocytic origin of the tumor, indicating that it was probably an amelanotic metastasis of the original malignant melanoma. The findings in this case demonstrate the potential usefulness of immunohistochemical microscopic characterization of specific intermediate filament proteins in the diagnosis of otherwise ambiguous cases of amelanotic melanoma.