MAP2K1 and cancer: Among the pan-cancers (n = 32) studied, MPM tumors from a cohort of 61 patients (n = 61) show the highest average protein level of p-MEK1 (Ser217/221), a marker of RAS/MAPK pathway activity (Fig. 1A), although its distribution in MPM samples is heterogeneous, suggesting that MEK1 activation occurs at least in at least a subset of MPM tumors.