NAPA, CALIF. – Because actinic keratoses are the most common lesions with premalignant potential in the skin, knowing how to predict their malignancy can be life saving, according to Dr. Miriam S. Bettencourt.
Most AKs do not progress to squamous cell carcinoma (SCC), but most invasive SCCs have evidence of preexisting AK, she said. Of the AKs that progress, 10% will metastasize, giving patients a 5-year survival rate, Dr. Bettencourt of the University of Nevada, Las Vegas.
"Major risk factors for AK malignancy include induration and inflammation, a diameter of over 1 cm, rapid enlargement, bleeding, erythema, and ulceration. Minor risk factors include pigmentation changes, palpability, pain, pruritus, and hyperkeratosis.
Hyperkeratotic AKs greater than 1 cm on the hands, wrists, or forearms have a 50% or greater risk for malignancy, she noted.
Other risk factors include age at diagnosis, human papillomavirus status, skin type, sunburns during childhood, proximity to the Equator, amount of outdoor activity, and a history of skin cancer.
Organ-transplant recipients have a 250-fold greater risk for developing AKs, and a 100-fold risk for SCC; 40% of organ-transplant patients with an AK will show progression to SCC, compared with 10% of the average population, she said.
However, the wide range of rates for the risk of AK progression to SCC found in the literature highlights the difficulty of putting risk into perspective, she noted.
In one study, of 169 patients with AKs, 65% developed an SCC from an AK; 97% of the patients had a contiguous AK near the site of the SCC ( Dermatol. Surg. 1995;21:184 ). But a review of 875 studies of AKs found a much lower rate; 11 studies were identified that predicted the risk of malignancy. The review found the rate to be 0.025% to 10% per lesion, per year ( Eur. J. Dermatol. 2006;16:335-9 ).
In another study, 10% of AKs were found to transform into SCC in 2 years ( Dermatol. Surg. 2007;33:1099-101 ).
A more recent report suggests that AKs also may progress to basal cell carcinomas (BCCs), she reported. In a study of 7,784 lesions on the face and ears of 169 patients, 65% of SCCs and 36% of BCCs arose in lesions that were previously diagnosed as AKs ( Cancer 2009;115:2523-30 ). The study also found the risk of progression of AK to SCC to be 0.6% at year 1 and 2.6% at year 4.
It is important to remember that risk applies to each individual AK and that the fate of any one AK is impossible to predict, said Dr. Bettencourt. "Although the risk [of progression] is small, since most [patients] have multiple AKs, the risk of transformation is much greater than the risk of any individual lesion."
She recommended treating all AKs because some may be difficult to distinguish from SCC and lentigo maligna.
Dr. Bettencourt reported being on the speakers bureaus of PharmaDerm and Graceway, and conducting clinical trials for 3M Pharmaceuticals.