Photocarcinogenesis promotion studies with benzoyl peroxide (BPO) and croton oil.

Previous studies demonstrated that BPO can promote chemically initiated tumor formation in SENCAR mice. In addition, a number of chemicals have been shown to promote and/or enhance UVR induced carcinogenesis. This study examined the effect of BPO on UVR initiated tumor formation. One hundred and forty-eight Uscd mice received 270 mJ/cm2 of UVB radiation to the posterior halves of their backs 3 times a week for 8 weeks. Four weeks later the mice were divided into 4 groups. Group I received croton oil in acetone applications to the back 5 times a week for the duration of the study. Group II received acetone, Group III received the BPO diluent, and Group IV received the BPO in an aqueous diluent applications as in Group I. One mouse in Group II (acetone) and one in Group IV (BPO) developed tumors in unirradiated skin. In the UVR initiated skin 38% of the survivors developed tumors in Group I (croton oil), whereas 5% did in Group II (acetone), 8% in Group III (BPO base), and 8% group IV (BPO). Thus under the circumstances of this study croton oil did promote UV initiated tumor formation but BPO did not. These results are consistent with those recently reported by Iversen.