ERBB2 and breast cancer: In another study by Creighton et al. [4], a signature of the MAP kinase pathway was defined from gene expression profiles of ErbB-2 (HER2), EGFR, Raf, and MEK in MCF-7 cells; this MAPK signature was found to share extensive similarities with signatures of ER-negative human breast cancer, which commonly has hyper-activated MAPK.