Skin precancer.

The document discussed the progression of skin cancers, particularly squamous cell carcinoma (SCC) and melanoma, from precancerous lesions. It highlighted the role of TP53 mutations in the development of SCC, noting that these mutations are more restricted in tumors than in precancers, suggesting additional selection processes. Melanoma development was described as a continuum from moles to more severe forms, with its genetics being less clear. Basal cell carcinomas (BCC) were noted to arise without precancers, involving TP53 and PTCH mutations. Sunlight exposure, particularly in childhood, was identified as a significant factor influencing the location and frequency of precancers, with genetic predispositions such as hair and skin color, DNA repair proficiency, and mole characteristics contributing to risk. The document also mentioned that immunosuppressant drugs and UV exposure could facilitate clonal expansion of precancers, while agents like 5-FU and retinoic acid had varying effects on regression and suppression of these lesions. The study of these mechanisms in both human and mouse models was beginning to provide a clearer understanding of precancerous events in the skin.