MAP3K1 and cancer: To overcome this lack of models we decided to deplete endogenous levels of MAP3K1 in BrCa cell lines already containing mPIK3CA. We considered gene depletion to be a surrogate model for MAP3K1 LoF mutations in tumors, since the majority of MAP3K1 genomic mutations found in cancer patients are scattered frame-shifts insertions/deletions [3, 4] and large chromosomal deletions [5] (i.e. LoF mutations).