It is important to note that a similar association between MAP3K1 and PIK3CA alterations with outcome on alpelisib were independently identified in a preliminary report from ASCO 2018.26 Although there are clear caveats to modeling the molecular effects of loss-of-function of MAP3K1 with PIK3CA mutations in breast cancer cell lines, we did not observe a direct effect of MAP3K1 loss on PI3K inhibitor sensitivity in vitro. Here, PIK3CA is linked to breast cancer.