Attempts to initiate skin tumours in mice in the 2-stage system using 4-chloromethylbiphenyl (4CMB), 4-hydroxymethylbiphenyl (4HMB), and benzyl chloride (BC). Report of the experiment at 10 months.

Groups of T.O. mice (Theiler's Original, derived from Swiss albino mice) were treated topically, with a single dose of 1.0 mg of 4CMB, 4HMB, or BC, or with 0.4 mg benzo[a]pyrene (B[a]P). Twice-weekly promotion of the treated skin area with croton oil was begun 1 week later. At 10 months the skin-tumour incidence in the positive control (B[a]P) was 8/19, with a mean latent period of 20 weeks. Both 4CMB and 4HMB have so far produced 1 papilloma each (1/36 at 40 weeks, and 1/39 at 34 weeks, respectively), while BC has produced none. Further time is required in order to ascertain whether these single papillomas will develop into carcinomas and thereby herald weak initiating activity for 4CMB and 4HMB.