The two most frequently mutated genes in breast cancer are PIK3CA and TP53. While TP53 showed comparable mutation rates between human breast cancer and MPA/DMBA-induced tumors (34% and 28%, respectively), PIK3CA mutation does not appear to be a common event in MPA/DMBA-induced tumors (35% in BC, 6% in MPA/DMBA). This evidence concerns the gene PIK3CA and breast cancer.