In contrast to our in vitro data, MEK1/2 inhibition alone had an immediate impact on tumor growth in both models, slowing the growth of WM266.4 xenografts and driving regression of A375 xenografts over the first 21 and 14 days of treatment, respectively (Fig. 5A; Supplementary Fig. S9A, S9F, and S9G). This evidence concerns the gene MAP2K1 and neoplasm.