BACKGROUND: The ability to clinically diagnose actinic keratoses (AKs) lesions has been taken for granted for some time. The importance of the malignant potential of these lesions is well known. However, a recent Phase IV, multicenter study assessing the long-term benefit of aminolevulinic acid-based photodynamic therapy provided a unique opportunity to prospectively examine the clinical histopathologic correlation of AKs. OBJECTIVE: The objective was to characterize the histopathology of clinically diagnosed AK lesions in the study population. METHODS: Punch biopsies of 220 clinically diagnosed untreated AKs were performed at baseline plus 51 lesions unresponsive to treatment (total, 271). RESULTS: Clinical diagnosis and histopathologic findings agreed in 91% (246/271) of the lesions biopsied. The balance of the biopsied lesions were: (1) benign changes 4% (11/271) and (2) occult cutaneous malignancy in 5% (14/271) of the cases, 12 squamous cell carcinomas and 2 basal cell carcinomas. CONCLUSIONS: In this study, about 1 in 25 clinically diagnosed AK lesions identified by board-certified dermatologist investigator(s) were occult early-stage squamous cell carcinomas on histologic assessment, a fact surmised by the medical community that until now had not been well quantified. These findings should be considered when clinicians decide how to treat and manage AK patients.
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