Diffuse melanosis in metastatic melanoma. Further evidence for disseminated single cell metastases in the skin.

Electron microscopy (EM) and electron microscopic cytochemistry have shown that diffuse melanosis in advanced metastatic melanoma is the result of an unlimited spread of single melanoma cells throughout the dermis; these cells retain their melanogenic capacity and continue to produce melanized melanosomes which eventually are deposited within dermal macrophages and thus impart to the skin a diffuse slate-blue color. These findings are in accordance with previous observations in a similar patient and thus support the concept that single cell metastasis represents a common pathogenic event in these patients.