PIK3CA and breast cancer: Oncogenic pathways and accompanying genes, such as PI3K/AKT, KRAS, MAPK, Wnt, β-catenin, BRCA2, ESR1, and P-cadherin, are generally up-regulated while tumor-suppressive pathways, such as p53, p16/INK4A, PTEN, and E-cadherin, are down-regulated in human and canine breast cancer (1).