PIK3CD and breast cancer: Consistently, a combinatorial drug screen of 42 compounds found that CDK4/6 inhibition exhibits the most significant synergism with PI3K inhibitors (BYL719 and GDC-0941) in a panel on PI3K-mutant breast cancer cell lines (T47D, MCF7, and MDA-MB-453) resistant to PI3K inhibition [192].