MAP2K4 and cancer: To further study a possible relationship between MAP2K4 mutations and responsiveness to MEK inhibition, we searched for additional MAP2K4 mutant cell lines in the well-annotated Sanger Center cell line panel.27 We identified an additional 6 cancer cell lines of different organ types (large intestine, ovary, endometrium, pancreas) with homozygous mutations in MAP2K4 (Supplementary information, Table S1).