UVA irradiation increases the incidence of epithelial tumors in UVB-irradiated hairless mice.

The interaction of UVA and UVB radiation in tumorigenesis in lightly pigmented hairless hr/hr mice was studied. Seventy-eight tumors (5 sarcomas, 4 squamocellular carcinomas, 1 carcinosarcoma, 63 papillomas, 2 keratoacanthomas, 1 fibrous polyp and 2 adnexal tumors) occurred in 12 mice receiving high UVA (582 J/cm2) plus high UVB(EE) (erythemally effective) (1.0 J/cm2) doses, whereas only 28 tumors (6 sarcomas, 1 carcinosarcoma, 20 papillomas and 1 keratoacanthoma) were found in 12 mice receiving low UVA (71 J/cm2) plus high UVB(EE) (0.8 J/cm2) doses. In 12 mice receiving low doses of both UVA and UVB(EE), only 2 tumors (sarcomas) occurred. The predominantly epidermal tumor response in the high UVA-high UVB group suggests that UVA irradiation increases the number of epithelial tumors when given together with carcinogenic doses of UVB radiation.