Myxoid malignant melanoma. A previously undescribed histologic pattern noted in metastatic lesions and a report of four cases.

Four patients are presented with malignant melanoma in which the stroma showed a prominent myxoid change. Since this peculiar feature had not been previously reported, metastatic lesions with this change caused considerable diagnostic confusion with other more commonly encountered myxoid tumors. On the basis of light microscopy, special stains, and electron microscopy, we demonstrated the melanomatous nature of the metastases and that the myxoid matrix is derived from reactive stromal cells rather than from the melanoma cells themselves. Three of the four patients had a history of primary melanoma; the longest interval between the primary lesion and the metastasis was 24 years.