ERBB2 and breast cancer: Analyses of the transcriptomic breast cancer dataset acquired by The Cancer Genome Atlas (TCGA) Program (30) further showed that, whereas the level of the MEK5 transcript was slightly higher, ERK5 level was similar in HER2− compared with HER2+ tumors, indicative of putative distinct mechanisms of ERK5 activation in different molecular subtypes of breast cancer (Fig. 1B).