The ultrastructure of benign pigmented naevi and melanocarcinomas in man.

: Nine benign pigmented naevi and 16 melanocarcinomas (malignant melanomas) were studied by light and transmission electron microscopy and the fine structure of benign and malignant melanocytes is described. It was found that malignant melanocytes generally exhibit a range of abnormalities of structure of nuclei and cytoplasmic organelles which distinguish them clearly from their benign counterparts. Of the abnormalities, those affecting the specific organelle of the melanocyte, the melanosome, were the most constantly present. No firm evidence was found for the existence of two types of melanosome or two types of melanocarcinoma. Although electron microscopy is capable of showing in great detail within individual melanocytes many changes which are clearly associated with malignancy, the technique does not appear to offer significant advantages over light microscopy in determining the diagnosis and prognosis in this group of conditions.