According to the latest American Society of Clinical Oncology/College of American Pathologists (ASCO/CAP) Guidelines for HER2 testing, HER2-negative breast cancers include tumors with HER2 IHC scores of 0, 1+ or 2+/ISH-negative1, for which treatment with traditional HER2-targeting agents has not demonstrated meaningful clinical benefits3,4. Here, ERBB2 is linked to breast cancer.