Cellular transformation phenomenon in human malignant melanomas

A cellular transformation phenomenon in keratinocytes based on electron microscopic studies of human cutaneous malignant melanoma is described. In contrast only minimal reactions of this kind were observed in lentigo maligna. The histologic features of the transformation were manifest first by striking enlargement of the nucleus and nucleolus as well as by changes in chromatin structures and the formation of nuclear bodies. The cytoplasmic reaction began with degradation at desmosomes and tonofilaments. A subsequent increase in the number of mitochondria was noted. Moreover, the cytoplasm contained numerous melanosomes, so many in fact that these cells were indistinguishable in their ultrastructure from true tumor cells. In addition to melanosomes, it is quite possible that nuclear substances, which may be responsible for the transformation, are transferred to the neighbouring keratinocytes.