Skin cancer and papillomaviruses in cattle.

We examined proliferative lesions on the sun-exposed, unpigmented skin of 13 cattle. Ages of animals at first examination ranged from 4 to 15 years, and 4 were observed for from one to 3 years, during which time progression to malignancy occurred in 2 of them. Early lesions consisted of keratin scales and horns; histology showed underlying acanthosis and hyperkeratosis. Advanced lesions were either squamous cell carcinomas or basaloid tumours with sebaceous and/or squamous differentiation; some were locally invasive but no metastases were found in the 6 animals that were available for necropsy. All 3 types of lesion could occur on the same animal. In early lesions from 11 of 12 animals, there was evidence for the presence of papillomavirus, either virions or viral DNA, the latter detected by gel electrophoresis and/or molecular hybridization. Viral DNA was also detected in 3 basaloid tumours and 2 squamous cell carcinomas from 4 animals. The DNA bound to a probe of bovine papillomavirus type 1 DNA under conditions of low stringency. We suggest that both infection with papillomavirus and exposure to sunlight, possibly in conjunction with other factors such as a period of photosensitization, are involved in the production of this spectrum of proliferative lesions, which bear some resemblance to human skin cancer.