Pathology and pathobiology of actinic (solar) keratosis - an update.

Actinic keratosis is a UV light-induced lesion and develops mostly in fair-skinned patients being susceptible to solar damage. The term actinic keratosis (AK) describes clinically ill-defined reddish to reddish-brown scaly lesions on erythematous base in areas damaged severely by sunlight. The term does not imply anything about the biology or histopathology. Actinic keratoses (AKs) have been recognized as precursor of cancer or of precancerous lesions in the past but today they are considered as an early in situ squamous cell carcinoma (1,2) and are categorized in several classifications with subdivisions into three grades depending on the amount of atypical keratinocytes in the epidermis.(3-6) The incidence of development of AK in caucasians increases with age, proximity to the equator and outdoor occupation. Australia has the highest skin cancer rate in the world. AKs are discovered in up to 40-50% of the Australian population older than 40 years.(7) AKs are the most common malignant lesion of the skin.(8-12).