The mitogen-activated protein kinase (MAPK), such as the classical MAPKs—extracellular signal-regulated kinases 1/2 (ERK1/2), ERK5, p38 isoforms, and the c-Jun N-terminal kinase (JNK) isoforms—have been strongly implicated in cancer progression, including breast cancer and EMT (6–9). The gene discussed is MAPK3; the disease is breast cancer.