The importance of ERK3 signaling in cancers has been recently recognized following our previous finding that ERK3 promotes cancer cell invasiveness by phosphorylating steroid receptor coactivator 3 (SRC‐3) oncoprotein and upregulating SRC‐3‐mediated transcription of matrix metalloproteinase (MMP) genes (Long et al., 2012). Here, MAPK6 is linked to cancer.