The MEK1/2-ERK1/2 pathway is a central signaling hub for multiple cell surface receptors, including TLRs, and the development of small molecules to inhibit the MEK1/2-ERK1/2 pathway has taken place over the last several decades predominately due to the high levels of over-activation of this pathway in several types of human cancer (Zhao and Adjei, 2014). Here, MAPK3 is linked to cancer.