H2AX and actinic keratosis: In fact, immunofluorescence analysis of surgically excised skin samples showed increased γ-H2AX levels in fibroblasts adjacent to premalignant (actinic keratosis; AK) and malignant (SCC) cancer lesions, in both of which CSL levels are decreased22,27, relative to fibroblasts of flanking unaffected skin (Fig. 2a, b and Supplementary Fig. 1a, b).