Actinic Keratoses Natural History and Risk of Malignant Transformation in the Veterans Affairs Topical Tretinoin Chemoprevention Trial

BACKGROUND: Actinic keratoses (AKs) are established as direct precursors of squamous cell carcinoma (SCC), but there is significant controversy regarding the rate at which AKs progress to SCC. The authors of this report studied a high-risk population to estimate the risk of progression of AK to SCC and to basal cell carcinoma (BCC) and the risk of spontaneous regression of untreated AKs. METHODS: Data were obtained from participants in the Department of Veterans Affairs Topical Tretinoin Chemoprevention Trial. Participants were examined every 6 months for up to 6 years. At each examination, the locations on the face and ears of clinically diagnosed AKs and lesions scheduled for biopsy were marked, and high-resolution digital photographs were taken, These photographs were used later to map and track the presence, absence, or biopsy of each AK across visits. RESULTS: In total, 7784 AKs were identified on the face and ears of 169 participants. The risk of progression of AK to primary SCC (invasive or in situ) was 0.60% at 1 year and 2.57% at 4 years. Approximately 65% of all primary SCCs and 36% of all primary BCCs diagnosed in the study cohort arose in lesions that previously were diagnosed clinically as AKs. The majority of AKs (55%) that were followed clinically were not present at the 1-year follow-up, and the majority (70%) were not present at the 5-year follow-up. CONCLUSIONS: In the current study, the authors quantified the malignant potential of clinically diagnosed AKs for both SCC and BCC, although many did not persist, and the results suggested that AKs may play a greater role in the overall burden of keratinocyte carcinomas than previously documented. Cancer 2009;115:2523-30. Published 2009 by the American Cancer Society.*