PIK3CA and breast cancer: Current phase I/II studies are being conducted using a combination of CDK4/6 inhibitor and PI3K inhibitors, such as the combination of LEE011 with fulvestrant and BYL719 or BKM120 in postmenopausal women with advanced HR+ breast cancer (Clinicaltrials.gov no: NCT02088684), and another study is looking at the combination of LEE011, BYL719 and letrozole (Clinicaltrials.gov no: NCT01872260).