Malignant melanoma and nevocellular nevi. Histogenesis and relationships. Fluorescence-microscopic and catamnestic photographic studies.

Investigations by use of the formaldehyde-induced fluorescence (FIF) method in benign and malignant pigment tumors of the skin are the main basis of the present monograph concerning the theory of the dualistic histogenesis of melanoma according to Mishima. Furthermore, the value of the FIF method in both classification and diagnosis of pigment-producing tumor cells after certain forms of therapy is emphasized. Experimental studies with nevus cell nevi have gained important findings on the histogenesis of nevus cells. These results indicate that nevus cells are possibly derivatives of normal melanocytes, for nevus cells in junctional nests still show a dendritic pattern like melanocytes. Based on photocatamnestic studies it can be concluded that the initial growth of melanoma may be very protracted. There are many indications that pigment spots which had sometimes existed for decades and were mistaken for nevi were malignant from the very beginning and had developed from the melanocytes of the epidermis. The development of melanomas on nevus cell nevi seems to be an exception. However, in these cases, too, malignant transformation occurs in the melanocytes of the epidermis overlying the nevus rather than in the nevus cells. This is confirmed by the findings obtained by the FIF method; under certain conditions dendritic cells may be demonstrated in all types of melanoma, which gives support to the unitary melanocytogenic origin of the tumor. However, typical dendritic tumor cells in great numbers are only visible in lentigo maligna. In the other tumors (e.g., SSM or NM), the shape of the tumor cells and the growth of the melanoma are probably dependent on the varying degree of cell dedifferentiation, the ability or unability for horizontal spreading growth as well as on terrain factors. However, there is every reason to believe that melanoma cells originate from melanocytes of the skin (or mucous membranes).