Tumorigenesis by short-wave ultraviolet A: papillomas versus squamous cell carcinomas.

The tumorigenic properties of UBV radiation (wavelengths 280-315 nm) are well established, in contrast to those of UVA radiation (315-380 nm). Very little information is available on the short UVA wavelengths (315-340 nm). To expand our knowledge on UVA tumorigenesis we investigated the development of skin tumours in albino hairless mice (SKH-hr1) exposed to custom-built experimental fluorescent tubes (EFL330) with spectral output centred around 330 nm. Two groups received continued daily exposures: one 56 kJ/m2 and the other 20 kJ/m2 per day. The third group was exposed to yellow fluorescent light devoid of UV, and served as a control. Each group consisted of 24 mice. Most of the mice in the high-dose group developed tumours; after 431 days 50% were tumour bearing. Two main types of tumours were observed: papillomas (Pap) and squamous cell carcinomas (SCC). In the low dose group only three mice attracted one papilloma each. No tumours were seen in the control group. Results show that the short-wave as well as the long-wave UVA contributes to carcinogenicity; the short wavelengths being approximately 5 times more efficient. The kinetics of tumour development under UVA exposure appeared to be different from that under UVB exposure. If, however, we exclude papillomas from our analysis, development is very much the same as with UVB irradiation, which yields predominantly SCC.