Reduction in lesions from Lmax: a new concept for assessing efficacy of field-directed therapy for actinic keratosis. Results with imiquimod 3.75%.

BACKGROUND Current parameters for assessing the efficacy of actinic keratosis (AK) treatments compare clinical lesions at the start and end of a study. However, the sun-exposed field also contains subclinical lesions which may become detectable during treatment. Lmax, the maximum lesion count during treatment, is a new concept to better assess the efficacy of field-directed AK therapies. Measuring efficacy using the reduction in lesions from Lmax includes for the first time the clearance of both subclinical and clinical lesions. OBJECTIVES To evaluate the reduction of lesions from Lmax to study end and compare the results with traditional efficacy endpoints using imiquimod 3.75% (IQ3.75%) as an example of field-directed AK therapy. MATERIALS & METHODS Pooled analysis of data from two 14-week, vehicle-controlled, double-blind studies of IQ3.75%. RESULTS With IQ3.75%, the median number of lesions increased from 10 at baseline to an Lmax of 22. The median absolute reduction in lesions to study end was 18 from Lmax versus 7 from baseline. The median percentage reduction in AK lesions to study end was 92.2% from Lmax compared with 81.8% from baseline. CONCLUSIONS The reduction in lesion count from Lmax is a novel efficacy parameter that should become the new way of evaluating field-directed AK therapies since it enables their efficacy against both clinical and subclinical lesions to be accurately determined. Together, the Lmax concept and IQ3.75% represent a new approach for the management of AK across a large sun-exposed field.