Effect of ultraviolet (UV) radiation and UVB-absorbing sunscreen ingredients on 7,12-dimethylbenz(a)anthracene-initiated skin tumorigenesis in hairless mice.

These experiments describe the enhancement of 7,12-dimethylbenz(a)anthracene (DMBA)-initiated skin tumorigenesis in hairless mice by subsequent chronic ultraviolet (UV) irradiation of the same skin site. Each carcinogen was administered at a level that separately resulted in threshold tumorigenesis. The cocarcinogenic response was evident as a marked increase in tumour incidence, tumour multiplicity and degree of tumour malignancy. Irradiation through the topically applied UVB (290-315 nm)-absorbing sunscreen ingredient, 2-ethylhexyl-p-methoxycinnamate, totally protected from the photoenhancement. However, irradiation through an alternative UVB absorber, octyl-N-dimethyl-p-aminobenzoate, failed to protect from photoenhancement. A possible immunologic role for the enhancement of DMBA tumorigenesis by UV radiation is proposed.