The development of actinic keratosis into invasive squamous cell carcinoma: evidence and evolving classification schemes.

Actinic keratosis is an incipient form of cutaneous squamous cell carcinoma. Consequently, actinic keratoses must be treated expeditiously to forestall their downward growth. Several classification schemes have been proposed to better categorize actinic keratoses, and to guide their diagnosis and treatment. Among these approaches is the "keratinocyte intraepithelial neoplasia" (KIN) system developed by Cockerell; Goldberg's concept of the "proliferative actinic keratosis" (PAK), and Berhane's emphasis on the "inflamed actinic keratosis" (IAK). In the future, disparate classification schemes may be unified into a single pragmatic approach which accurately reflects the biological process whereby actinic keratoses devolve into invasive squamous cell carcinoma.