DIFFERENCES IN LATENCY AND INDUCIBILITY OF MOUSE SKIN MELANOMAS DEPENDING ON THE AGE AND ANATOMIC SITE OF THE SKIN

To determine whether the occurrence of skin melanoma is influenced by the age or the anatomic source of the skin in melanoma-susceptible tra nsgenic mouse models, skin was grafted from donors of different ages o r from different anatomic sites to a standard (lateral trunk) site in adult recipients of the same transgenic strain. In 27 grafts of neonat al body skin, melanomas arose with a significantly shorter latency tha n in 37 grafts of older body skin, The difference may reflect not only the larger number of extrafollicular melanocytes in a given area of n eonatal skin but also their unusually high mitotic activity shortly af ter birth and the influence of other growing skin cells nearby, Each o f these body-skin grafts usually developed a single tumor situated nea r the graft edge, Because maximal wound healing occurs at the edge of such full-thickness skin grafts, melanocytes near the edge would recei ve the highest exposure to growth factors and cytokines associated wit h wound healing, In contrast to these results, grafts of snout skin yi elded many melanomas, each originating from melanocytes within a vibri ssa follicle rather than at the graft edge. The relatively strong loca l tumorigenic stimulus may be attributable to intrafollicular growth f actors normally involved in whisker growth. The above-described experi ments support the conclusion that agents in the immediate skin environ ment of the melanocyte, in addition to the state of the melanocyte its elf, contribute to melanoma formation.