Proliferative actinic keratosis.

BACKGROUND: Solar/actinic keratoses (AKS) are premalignant lesions, usually less than 1 cm in diameter, that appear on chronically sun-damaged skin.

METHODS: We describe four patients with a form of AK that enlarged and recurred despite standard treatment. Histologic examination revealed a single and multilayered sheet of anaplastic cells along the undersurface of the epidermis extending down hair follicles and present over a large area.

RESULTS: Three of the patients developed either a squamous cell carcinoma (SCC) or basal cell carcinoma (BCC) within the area encompassed by the AK.

CONCLUSIONS: These cases represent an insidious, proliferative form of AK with an increased tendency to develop into skin cancer.