NRG1 and cancer: We next examined localization of heregulin, EGFR, ErbB2, ErbB3, ErbB4, pEGFR, pErbB2, pErbB3 and pErbB4 proteins by immunohistochemical analysis.Heregulin immunoreactivity was predominantly observed in the cytoplasm of cancer cells in 72 cases (46%; 31% with score 8, 9% with score 9 and 6% with score 12) (Figure 2A).