MYC and breast cancer: When compared to Myc overexpressing females, double mutants (both MMTV-Myc;Pik3caE545K/+;WAPCre and MMTV-Myc;Pik3caH1047R/+;WAPCre) develop focal mammary tumours much quicker, within 1 week of the first parturition, compared to 115 days after first parturition [67].