ERBB2 and breast cancer: The American Society of Clinical Oncology (ASCO) and the College of American Pathologists (CAP) have developed guidelines for HER2 amplification in breast cancer: an absolute HER2 gene copy number lower than four or HER2/CEP17 ratio of <1.8 is considered HER2 negative (HER2–), an absolute HER2 gene copy number between four and six or HER2/CEP17 ratio between 1.8 and 2.2 is considered HER2 equivocal, and an absolute HER2 gene copy number greater than six or HER2/CEP17 ratio >2.2 is considered HER2 positive (HER2+) [44].