MAP2K4 and breast cancer: To study whether the MAP3K1 and MAP2K4 mutations identified in breast cancers give rise to a vulnerability that can be exploited therapeutically, we used a panel of breast cancer cells lines that we sequenced previously.12 Among the 11 breast cancer cell lines, we found that MDA-MB-134VI and MPE600 had inactivating mutations in MAP2K4 (Supplementary information, Table S1).