ERBB2 and breast neoplasm: The results obtained from the present study suggest that some HER2+ breast tumors may not respond to HER2-signal inhibitors because they do not actually exhibit increased HER2 signaling activity or functional dependence on HER2 signaling, whereas some HER2- breast tumors could benefit from HER2-signal inhibitors because the HER2 pathway is abnormally active in these tumors.