MAP2K1 and neoplasm: We found that B16F10 tumours treated with MEK1‐hi EVs (derived from 9609 fibrosarcoma cells) were 51% and 46% smaller in area (p < 0.05 Figure 3d) and weight (p < 0.1 Figure S8c) than tumours treated with vehicle control or MEK1‐low EVs, respectively.