In mice studies targeting TGF-β1 transgene, primarily in the suprabasal/differentiated layers of the epidermis in transgenic, overexpression of TGF-β1 inhibits papilloma formation at early stages but promotes tumour aggressiveness via epithelial–mesenchymal transition at later stages of skin carcinogenesis (Weeks et al, 2001). This evidence concerns the gene TGFB1 and papilloma.