MAPK3 and breast cancer: Although the EGF/Raf/MEK1/2/ERK1/2 pathway has been investigated with respect to cancer cell metastasis, and it is known that the activation of ERK1/2 promotes the growth of breast cancer cells [12], the effect of ERK1/2 signaling activation on the metastasis of invasive breast ductal carcinoma is poorly characterized and remains of interest.