ERBB2 and breast cancer: The molecular characterization of the Type 1 genes (e.g. ESR, HER2) suggests the development of therapies for ER+/PR+ and HER2+ would be effective for these breast cancer subtypes, however ~15-20% of the breast cancer tissues expressing low levels of these biomarkers (i.e. triple negative subtype) have poor prognosis and few treatment options.