MAPK3 and fibrosarcoma: For instance, nitrosamines' influence on EGFR signaling can induce changes in the cyclic adenosine monophosphate-protein kinase A-rapidly accelerated fibrosarcoma-mitogen-activated protein kinase kinase-extracellular signal-regulated kinase 1/2 (cAMP-PKA-RAF-MEK-ERK1/2) axis, subsequently promoting cancer cell proliferation.