PIK3CD and breast cancer: Cai et al., using a whole-genome screen on HR+ PIK3CA-mutated BC cell lines, found that the loss of several genes (TSC1, TSC2, TBC1D7, AKT1S1, STK11...), which negatively regulate mTORC1, conferred resistance to PI3K inhibitors, and confirmed that mTOR inhibition could overcome resistance.