PTEN and breast cancer: A broad range of tumor types, including breast cancer, are characterized by activating mutations of PIK3CA (the gene encoding for p110α, a member of the class I group) and its downstream effector AKT1, as well as inactivating mutations of phosphatase and tensin homolog (PTEN), the gene encoding the lipid phosphatase that counteracts the action of PI3Ks [6].