ULTRAVIOLET-RADIATION A-INDUCED PRECURSORS OF CUTANEOUS MELANOMA IN MONODELPHIS-DOMESTICA

Two groups of 30 dorsally shaved opossums (Monodelphis domestica) were exposed three times per week for 81 weeks to 250 J/m(2) of UV radiati on from FS40 sunlamps (similar to 150 J/m(2) of UV radiation B; UV-B), or to 2.5 x 10(4) J/m(2) of UV radiation A (UV-A) from filtered F40BL B fluorescent lamps (black lights). Animals were monitored for the app earance of nonmelanoma skin tumors (NMSTs) and melanocytic hyperplasia (MH). After 81 weeks of exposures, the prevalence of NMSTs was 71% an d 4% for animals exposed to UV-B and UV-A, respectively. The differenc e between the treatment groups was statistically significant (P < 0.00 1). However, the prevalence of MH in the treatment groups, 31% for UV- B-exposed animals and 22% for UV-A-exposed animals, was not significan tly different (P > 0.05). Thus, a dose of UV-A that was relatively ine ffective in producing NMSTs, compared to UV-B, was an effective as UV- B in the induction of MH. If, as shown previously, MH is the precursor lesion for melanoma in this model, these results suggest that the act ion spectra for the induction of melanoma and NMSTs in the opossum are different.