Cytomorphology of metastatic melanoma--use of S-100 protein in the diagnosis of amelanotic melanoma.

The cytomorphological features of cells from 52 cases of metastatic melanoma obtained by fine needle aspiration cytodiagnosis were studied. Morphologically, 11, 19 and 22 cases were classified as spindle, epithelial, and mixed cell types of metastatic melanoma respectively. There were 34 melanotic and 18 amelanotic melanomas. Besides melanin, the presence of intranuclear cytoplasmic inclusions, eosinophilic macronucleoli and giant cells were helpful in the diagnosis of a melanoma. Where attempted, staining for S-100 protein was positive in all the 19 cases (eight amelanotic and 11 sparsely pigmented melanomas). In addition eight cases of metastatic tumour where a differential diagnosis of poorly differentiated carcinoma or large cell lymphoma was entertained, were also studied for localization of S-100 protein and all were found to be negative. Electron microscopy was performed in five cases and showed the presence of melanosomes and/or premelanosomes.