Human malignant melanoma heterotransplanted to nude mice.

Five different human malignant melanoma were heterotransplanted subcutaneously to nude mice. When small tissue pieces were used 3 out of 5 tumors grew. Subcutaneous injections of suspended tumor cells were also made, but all failed to take. Metastatic or infiltrative growth was never seen in the mice observed for up to 2.5 months. The successful grafts largely retained the original morphologicaL features. The three successfully transplanted tumors could all be serially transferred with 100% tumor take. In one case passage time was reduced from 40 days to 15 days. As measured with 3H-thymidine incorporation the proliferation rate increased during the passages. These changes might be due to a selection of more rapidly growing tumor cells in the nudes.