PIK3CB and breast cancer: Taselisib, a β-isoform-sparing pan-PI3K inhibitor, when combined with fulvestrant in the treatment of PIK3CA-mutated ER+/HER2– locally advanced or metastatic BC, showed only a moderate 2-month improvement in median PFS (7.4 vs. 5.4) over the placebo arm (Baselga et al., 2018).