Solar keratoses.

Solar keratoses are premalignant epidermal lesions that rarely transform to squamous cell carcinoma and occur even in temperate European climates much more frequently than has been previously supposed. Some lesions of solar keratosis may spontaneously regress due to immune rejection, but immunological influences do not appear to be responsible for keeping them from progressing to frank malignancy. Their frequency, accessibility and various morphological forms provide the basis of excellent models for carcinogenesis.