Background: Controversy exists over the rate of malignant transformation of actinic keratoses (AKs) and, therefore, which treatment is indicated. Furthermore, it is not known to what degree each of the separate clinical subtypes of AKs become malignant. Objective: Our purpose was to examine clinically diagnosed hyperkeratotic AKs and classify them histologically. Methods: Fifty papular hyperkeratotic AKs on the dorsum of the hand, wrist, and arm, less than 1 cm in diameter, were identified in 43 patients. Histologic evaluation was conducted in a blinded fashion by two observers. Results: Histologic examination showed 18 lesions (36%) to be invasive squamous cell carcinoma, whereas another seven (14%) were squamous cell carcinoma in situ. Proliferative AKs were the next most common lesion identified (26%), followed by hypertrophic (10%) and lichenoid (4%) AKs. Basal cell carcinomas (4%) and other benign lesions (6%) comprised the rest of the biopsy specimens. Conclusion: It is possible to predict clinically, with greater certainty than previously realized, which AKs have a greater tendency toward malignant change. Clinical hyperkeratotic AKs less than 1 cm in diameter on the dorsum of the hand, wrist, or forearms of white patients have a malignancy rate of 50%. Lesions with this clinical description should be removed by shave biopsy, then by 35% trichloroacetic acid, then liquid nitrogen to a width and depth of 3 mm.
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