Histologic parallels between mastocytoma and melanoma. Demonstration of melanin in tumor cells of mastocytoma and metachromasia in tumor cells of melanoma

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Abstract
A series of primary canine mastocytomas, canine melanomas, and human melanomas was studied. A majority of the melanomas contained some tumor cells with meta-chromatic granules; a majority of the mastocytomas contained some tumor cells with pigment granules, which were shown to be primarily melanin by means of differential staining. The metachromasia of the granules in the tumor cells of melanoma appeared to be due to the presence of both acid mucopolysaccharides and RNA in varying proportions. The metachromasia of the granules in the tumor cells of canine mastocytoma and in the mast cells of urticaria pigmentosa also appeared to be produced by the composite effect of both acid mucopolysaccharides and RNA. In addition to similarities in granulation, other parallels in the appearance and arrangement of the tumor cells were demonstrated in canine mastocytoma and canine melanoma. The findings of this study add to the evidence that mast cells are capable of melanin synthesis and are histogenetically related to melano-cytes. It is suggested that nevi and melanomas are histogenetically related to canine mastocytomas.