PAK5 and cancer: It is well‐established that MEK undergoes phosphorylation and activation, facilitated by members of the RAF family (A‐, B‐, and C‐RAF) and the p21‐activated kinase (PAK) family.[11] Among these proteins, only the activities of B‐RAF and PAK5 were consistent with MEK activation in all three cell lines (Figure 1C,D), suggesting that B‐RAF and PAK5 are potential upstream kinases that control MEK activation in RNF43‐mutated cancer cells.