PTEN and breast cancer: To investigate a possible role for ATM-dependent PTEN phosphorylation in breast cancer, we bred the Pten398A allele on the background of mice expressing the inactivated neu (Erbb2) fusion gene under the transcriptional control of the mouse mammary tumor virus (MMTV) promoter/enhancer [34] (MMTVneu, Supplementary Fig. 1B).