AKT1 and breast cancer: However, Pipp ablation in an MMTV-PyMT mouse model of breast cancer promotes mammary tumour initiation and growth resulting in larger tumours compared with mice expressing Pipp. PyMT;Pipp−/− mice also exhibit increased AKTSer473 phosphorylation in both hyperplastic foci and primary mammary tumours suggesting that Pipp loss enhances oncogene-driven breast cancer initiation and progression via regulating PI3K/AKT signalling.