Activated Ras activates a RAF (Rapidly Accelerated Fibrosarcoma) family protein (ARAF, BRAF and CRAF rapidly accelerated fibrosarcoma proteins), which in turn phosphorylates and activates MEK (mitogen-activated protein kinase kinases MEK1 and MEK2, also known as MAP2K1 and 2 or MAPKK 1 and 2), and MEK phosphorylates and activates the mitogen-activated protein kinase (MAPK/ERK). Here, MAP2K1 is linked to fibrosarcoma.