MAP2K1 and neoplasm: Neurofibromin 1 (Nf1) is a tumor suppressor gene that encodes a RAS–guanosine triphosphatase–activating protein (RAS-GAP) that reduces RAS activity and inhibits mitogen-activated protein kinase 1/2–extracellular signal-regulated protein kinase 1/2 (Mek1/2-Erk1/2) downstream signaling23.