The kinetics of skin cancer: progression of actinic keratosis to squamous cell carcinoma.

BACKGROUND Actinic keratoses (AKs) are intraepidermal skin tumors that have the potential to progress to squamous cell carcinomas (SCCs). SCCs are the second most common cancer with more than 200,000 cases each year in America. Approximately 10% of AKs will progress to SCCs. This progression is thought to be due to chronic sun exposure, specifically ultraviolet B sunlight. OBJECTIVE Understanding the kinetics of this developmental process can help physicians better evaluate and subsequently treat precancerous AKs. METHODS To determine the time scale of AK progression, we conducted a retrospective electronic medical record study of all patients diagnosed histopathologically with an SCC between July 1, 2003, and June 30, 2005. RESULTS Of a total patient population of 6,691, 91 had a histopathologically confirmed diagnosis of an AK at the same site as the subsequent SCC. The length of time for an AK to progress to an SCC was determined to be 24.6 months (95% confidence interval, 21.04-28.16 months). CONCLUSIONS Although a more controlled in vivo study is indicated, these data provide a good estimate of the time course from an AK to an SCC. In summary, of the estimated 10% of AKs that will develop into an SCC, the progression will take approximately 2 years.