MAPK6 and breast cancer: Several different molecular mechanisms underlying the cancer‐promoting role of ERK3 have been proposed, such as activating SRC‐3/PEA3‐mediated matrix metalloproteinase (MMP) gene transcription in lung cancers and breast cancer [3] and c‐Jun/AP1‐mediated IL‐8 expression in colon cancer cells and MDA‐MB231 breast cancer cells [9].