[Correlation between differentiation and malignancy in human malignant melanocytes "in vivo" and "in vitro" (author's...

The relationships between differentiation and malignant transformation were studied in human malignant melanomas in vivo and in vitro. Melanocyte differentiation was assessed by ultrastructural morphological characteristis (the appearance of the melanosomes and related structures) localization of dopa-oxidase and assay of 5-S-cysteinyldopa, a specific metabolite. The transformed characteristic of the cells in vitro was evaluated by their ability to give rise to established cell lines, karyological modifications and heterotransplantation in Nude mice and Syrian hamsters. Morphological variability of the cells in malignant melanomas is accompanied by variability in the localization of dopa-oxidase, the level of 5-S-cysteinyldopa, chromosome pattern and their heterotransplantibility. The lack of pigmentation in some malignant melanoma lines can result from either an irreversible loss of some functions which give rise in melanization and the malignancy in maintained, or by phenomenon of regulation determined by intra or extra-cellular factors with the loss of heterotransplantability. Modulation phenomena affecting tumorigenicity and pigmentation although sometimes concomitant are not identical.