THE ORIGIN OF THE MALIGNANT MELANOMATA

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Abstract
There are 3 types of cells characteristic of malignant "melanomata. Firstly, the naevus cell: this is polymorphic in outline with little cytoplasm and a dark nucleus. Individual naevus cells are separated by varying amts. of connective tissue. These cells may be derivatives of the sensory nerve . end apparatus. Secondly, the epithelial cell: this has abundant cytoplasm and a large pale vesicular nucleus. The epithelial cells are closely aggregated and are downgrowths of the surface epithelium. Thirdly, the branched chromato-phore: this is a pigment carrying cell and the pigment is clumped into masses of irregular size and shape. This differentiates it from a pigment producing cell which is pigmented uniformly. The dopa positive reaction is obtained normally only in epidermal cells, but cells of the mongol spot which are chromatophores of mesodermal origin also give the reaction. Melanomata may be seen originating from the pigment epithelium of the retina, ciliary body or iris. Melanomata may be found in the choroid. It is known, however, that retinal pigment and choroidal pigment are morphologically and embryologically separate entities. In naevi of the uveal tract there are no naevus cells. In certain melanomata naevus and epithelial cells may proliferate side by side. These facts cannot be reconciled with a unitary theory for the origin of melanin or malignant melanomata. The growths may arise from any or all of the 3 typical cells.