GEM models driven by the mouse mammary tumour virus (MMTV) promoter were used to characterise the effects of several now widely accepted oncogenes and tumour suppressors in BC (including tumour suppressors Pten, Brca1 and Trp53 and oncogenes Erbb2, Myc and Ccnd1) (Vargo-gogola & Rosen 2007). Here, PTEN is linked to breast cancer.