Among the most frequently dysregulated pathways in breast cancer are the phosphatidylinositol 3-kinase (PI3K) pathway and the Ras/MAPK pathway [2,27,28,29,30,31,32,33,34,35,36,37,38,39], and therefore we chose to manipulate one component of each pathway (i.e., PTEN deletion and KRAS(G12V) expression) to promote pathway activation. This evidence concerns the gene KRAS and breast cancer.