Strain difference of mouse skin tumorigenesis was studied with 12-O-tetradecanoylphorbol-13-acetate (TPA) and benzoyl peroxide (BzP) both in 8-week-old hypocatalasemic C3H mice (C-s(b)) and in normal C3H/HeNCrj mice (C3H). Two weeks after initiation by 4 mu mole MNNG, both strains of female mice were promoted by 10 nmole TPA or 10 mg, 20 mg BzP twice weekly for 30 and 52 weeks. The incidence of skin tumors in C-b(s) was significantly increased as compared to that in C3H mice promoted by TPA for 30 weeks but after 52 weeks of TPA promotion there was no difference between the 2 strains. By the promotion with 10 mg or 20 mg BzP, the incidence of skin tumor in C3H was 5% at both levels after 30 weeks of promotion and 19% and 38%, respectively, after 52 weeks of promotion. No skin tumors appeared in C-b(s) mice with BzP treatment after 30 weeks of promotion. After 52 weeks of promotion by 10 mg BzP, skin tumors were induced in only 15% of C-b(s) mice. The results show that genetic factors, especially radical scavenging enzymes, controlled susceptibility to skin tumorigenesis by promotion with either TPA or BzP.

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