ERBB2 and breast cancer: We quantified human epidermal growth factor receptor 2 (HER2) RNA and protein expression in 2018 American Society of Clinical Oncology/College of American Pathologists (ASCO/CAP) in situ hybridization (ISH) group 4 (HER2/centromeric probe 17 (CEP17) ratio <2.0, average HER2 copy number ≥4.0 and <6.0, and 2013 ASCO/CAP ISH equivocal) breast cancers.