Enhancement of chemical carcinogenesis in mice by systemic effects of ultraviolet irradiation.

The present study was designed to determine the systemic influence of ultraviolet (UVB) irradiation upon subsequent carcinogenesis induced by benzo(a)pyrene. The source of UV irradiation consisted of six Westinghouse FS-40 fluorescent sunlamps. Female BALB/c mice received five 30-min dorsal UVB radiation treatments per week for 13 wk. At the end of 13 wk, irradiated and unirradiated mice received ventral applications of 0.1 or 1.0 mg of benzo(a)pyrene twice weekly for 20 or 10 wk, respectively. At 18 wk after the first benzo(a)pyrene treatment, mice receiving 0-, 0.1-, or 1.0-mg benzo(a)pyrene treatments bore 0, 12, or 29 tumors per group of 18 mice, respectively. Tumor-free survival was significantly shortened in the UV-irradiated hosts as compared with unirradiated hosts, as analyzed by the Kaplan-Meier method of survival analysis. Therefore, ultraviolet irradiation induced a systemic effect which enhanced subsequent tumor induction by benzo(a)pyrene in a manner which was dependent on the dose of benzo(a)pyrene.