Identical twins and a fraternal triplet were studied because the identical twins developed malignant melanoma at age 53. Each had a preexisting mole, nearly identically placed on the left chest, which began to grow within 2 months of one another. The homozygosity of the twins was established with high probability by appearance, behavior, psychologic testing, deficiency of color vision, red cell typing, haptoglobin typing, dermatoglyphics, lymphocyte typing, mixed lymphocyte culture, lymphocyte transfer, and skin grafting. The concordance for cutaneous malignant melanoma as well as the congruence for the site and identity of age of onset of this tumor in these monozygotic twins clearly indicates the predominant role of genetic rather than environmental factors in the development of their cancers (congruent contemporaneous concordance). Furthermore, the observation suggests that the initial phenomenon eventually leading to malignant melanoma occurred in the conceptus prior to twinning. This finding is relevant to understanding the etiopathogenesis of malignant melanoma in man.

In the present work the carcinostatic effect of exogenous D-galactosamine on Sarcoma-180 and Ehrlich ascites carcinoma cells was examined in vitro. D-galactosamine exhibited a powerful anti-tumor efect on these tumor lines, resulting in a rapid loss of viability and transplantability. The toxic effect of D-galactosamine was not altered by addition of glucose or pyruvate. The effects of galactosamine were evident histologically even before the cells became stainable by trypan blue.The biochemical basis for the cytotoxic effect of galactosamine, at a concentration used for viability, transplantability and tissue-culture study, was investigated. Galactosamine was taken up very rapidly by the tumor cells, reaching a steady state rate within 60 min. Fifty-three pmoles of galactosamine were accumulated by los cells. About