TP53 and breast cancer: Given this and also the co-occurrence of PIK3CA and TP53 mutations in human breast cancers, we developed a Pik3caH1047R;Trp53R270H;MMTV-Cre double mutant model by crossing the Pik3caH1047R;MMTV-Cre mice with Trp53R270H flox mice [12].