PTEN and breast cancer: As mentioned before, PI3K pathway alterations occur in about 70 % of breast cancers and include mutations and/or amplifications of the genes encoding the PI3K catalytic subunits, p110α (PIK3CA) and p110β (PIK3CB), the PI3K regulatory subunit p85α (PIK3R1), and the PI3K effectors AKT1, AKT2, and PDK1. The loss of lipid phosphatases such as PTEN can also activate the pathway [17, 39–42].