Rough patches on the skin that can turn into squamous cell carcinomas may also set the stage for basal cell carcinomas.

The patches, called actinic keratoses (AKs), are caused by UV radiation and are one of the most common conditions treated by dermatologists. Treatment is primarily for cosmetic purposes and symptom relief (AKs can be tender and itchy) but also to prevent malignancy. AKs are generally considered precursors of squamous cell carcinoma, a treatable form of skin cancer. However, the frequency at which this transformation occurs is under dispute, with various reports putting the rates as low as 0.025% and as high as 20%.

Researchers evaluated data from approximately 7,784 AKs on the faces and ears of 169 patients from the Oklahoma City VA Medical Center who were at high risk for skin cancers. These individuals had been examined every six months for six years as part of another larger trial on skin cancer chemoprevention.

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The risk of AKs progressing to squamous cell carcinomas was low, but about 65% of all the primary squamous cell carcinomas diagnosed arose from AK lesions. The researchers found the same to be true for 36% of all the primary basal cell carcinomas as well.

Basal cell carcinomas—the most common form of skin cancer in the United States—had not previously been connected to AKs. Investigators acknowledge that some of those basal cell carcinomas could have been mistaken for AKs initially. Nevertheless, they “suggest that the role of clinically defined AK in the overall burden of [keratinocyte carcinomas] may be greater than previously appreciated” (Cancer. 2009; 115:2523-2530).