PIK3CA and breast cancer: In particular, mutations in genes encoding proteins upstream of mTORC1, including core components of the PI3K/AKT pathway (i.e., PIK3CA, which encodes the p110α subunit of PI3K, PTEN and AKT1) and the MAPK pathway (MAP3K1, MAP2K4, BRAF and HRAS) are frequent in BC and PC and considered to be drivers of tumourigenesis [49,50,51].