Non-melanoma skin cancer and solar keratoses. I. Methods and descriptive results of the South Wales Skin Cancer Study.

This study aimed to describe the prevalence and incidence of solar keratoses and skin cancers and the natural history of solar keratoses in a random population sample. It was a cross-sectional study, with follow-up, conducted in South Wales, and involved 1034 subjects aged 60 years and over drawn from the Family Health Services Authority register. The main outcome measures were detection of the presence of solar keratoses and skin cancers on sun-exposed skin and photographic validation of solar keratoses and biopsy confirmation of cancers wherever possible. We found that solar keratosis prevalence was 23% (95% confidence interval 19.5-26.5) and that of skin cancer (all types) 2% (95% confidence interval 1.0-3.5). The incidence rate of solar keratoses was 149 lesions per 1000 person-years and of non-melanoma skin cancer 9 per 1000 person-years. In all 21% (95% CL 16-26) of solar keratoses regressed spontaneously during follow-up. None underwent malignant change. We believe that the failure of individuals to seek medical advice and the variable under-registration of non-melanoma skin cancer makes population-based study important. The high prevalence and incidence of malignant and pre-malignant skin lesions in this random sample raise major public health concerns. The high rate of spontaneous regression of solar keratoses and the low rate of malignant change challenges conventional views about the need for routine treatment of these lesions.