ERBB2 and breast cancer: The American Society of Clinical Oncology (ASCO)/College of American Pathologists (CAP) HER2 testing guidelines in BC, initially published in 2007, and updated in 2013 and 2018, have been focusing on separating patients with HER2 positive tumors who are eligible for HER2-targeted therapy, from those with HER2 negative tumors [1,2,3].