Before tumor formation, Cav-1 null mice develop extensive epidermal hyperplasia in response to DMBA treatment. We also examined the morphology of the skin at 7 weeks of DMBA treatment, just before the development of tumors. Skin tissue samples were excised, formalin-fixed, paraffin-embedded and stained with H&E. Note that in wild-type animals, there is only a modest increase in thickness of the epidermal layer, as compared with non-treated animals (Figure 1) . In contrast, in Cav-1 null mice there is a dramatic increase in the thickness of the epidermal layer, ie, severe epidermal hyperplasia. Medium- and high-power views are shown in A and B, respectively. Images were acquired with a 20× objective (A). Boxed areas in A are shown further magnified in B. Note that in Cav-1 null mice all of the layers of the epidermis, especially the basal, granular, and cornified layers are hyperplastic or thickened.