Inhibition of two-stage carcinogenesis in mouse skin with bis(2-chloroethyl)sulfide

ICR/Ha Swiss mice, 30 females/group, were given a single application of 20 mug 7,12-dimethylbenz(a)anthracene, followed 2 weeks later by three times weekly applications of phorbol myristate acetate (PMA), 2.5 mug/application. In the accompanying inhibition experiments, sulfur mustard [SM; bis(2-chloroethyl)sulfide] was applied at a dose of 20 mug/application during the promotion phase, either on the same day as PMA, i.e., three times weekly, or on alternate days, i.e., twice weekly. The experiments were continued for 385 days. The control group, i.e., without SM, resulted in 27 of 30 mice with a total of 281 papillomas. Sixteen of these mice also bore squamous cell carcinomas. In the two groups also receiving SM, two or three times weekly, 2 of 30 and 1 of 30 mice, respectively, bore papillomas. Carcinomas were not observed in these groups. The inflammatory response of mouse skin to the combined treatments of SM and PMA was no greater than with PMA alone.