The third scenario is that the target cell of transformation is a multi-potent progenitor with the ability to undergo differentiation into multiple epithelial lineages, or even mesenchymal lineages (for example, DMBA-induced and Brca1Co/Co;TgMMTV-Cre;p53+/-); support for this hypothesis comes from Keratin IF analyses in which, even within a histologically homogenous tumor, two types of epithelial cells are present (Figures 2g-k). This evidence concerns the gene TP53 and neoplasm.