Development of early melanocytic lesions in transgenic mice predisposed tomelanoma

We have previously described a line of transgenic mice (TG3) that spontaneo usly develops heritable malignant melanoma. Histological analysis of these animals during the first postnatal month is described here. In the TG3 line , the number of melanocytes is increased at all anatomical sites to which n eural-crest-derived melanocytes normally migrate. Clonal expansion and morp hological changes of these melanocytes can be detected as early as postnata l day (PND) 15. By PND 30, cells morphologically indistinguishable from the tumor cells of adult transgenic mice were detected in the ear, eye lid and perianal region. These cells are believed to be the precursors of the prim ary tumors in adult mice. The stepwise development of melanoma in the TG3 l ine is similar to the stepwise development of melanoma in humans.