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Two biologically and clinically different malignant melanomas are found in man. As compared to the malignant melanoma developed from junction nevus, the melanoma developed from Dubreuilh's precancerous melanosis has a slower rate of growth, metastasis and invasiveness. Furthermore, in contrast to melanoma of junction nevus origin, melanoma from Dubreuilh's melanosis is radiosensitive and does not assume the amelanotic form. Not only the malignant melanomas but also the premalignant stages exhibit differences. Dubreuilh's precancerous melanosis, in contrast to junction nevus, is a condition which occurs during later life in exposed areas, is radiosensitive and has a high incidence of malignant transformation. Cellular and subcellular differential characteristics expressing enzymic and ontogenic differences of these two melanomas are described. The author proposes that in the future we consider human malignant melanoma to be not one but two diseases—melanocytic malignant melanoma and nevocytic malignant melanoma. These may be called malignant melanocytoma and malignant nevocytoma, respectively.
Yutaka Mishima (Sun,) studied this question.