Myth: Hypertrophic actinic keratoses are more likely to progress to squamous cell carcinoma
Actinic keratosis (AK) indicates cumulative UV exposure and is the initial lesion in the majority of invasive cutaneous squamous cell carcinomas (SCCs). However, most AKs do not progress to invasive SCC and it currently is not possible to clinically or histopathologically determine which AK lesions will progress to SCC.
The rates of progression of individual AK lesions to SCC vary. In 2011, Feldman and Fleischer summarized 6 studies of 560 to 6691 patients with AK. The AK progression to SCC was found to range from 0.075% per year per lesion to 14% over 5 years.
Criscione et al found that the risk of progression of AK to primary SCC was 0.60% at 1 year and 2.57% at 4 years. In this study, 187 primary SCCs were diagnosed after enrollment, with 65% arising in previously clinically diagnosed and documented AKs. Therefore, although the authors noted low risks of progression of AK to SCC, they observed that the majority of SCCs arose from AKs.
The risk for progression of AK to invasive SCC with the potential for metastasis warrants treatment of AK with lesion- or field-directed therapy or a combined approach when indicated. Dermatologists also should monitor AK patients closely.
It’s a myth that hypertrophic lesions are more likely to turn into SCC. In fact, it’s the lesions with follicular extension that are more likely to progress to SCC. These may be hypertrophic or atrophic or simple AKs. The genetics of AKs that become hypertrophic may be different from those that become invasive. These lesions may be more likely to first grow outward before becoming invasive.
—Gary Goldenberg (New York, New York)