ERBB2 and breast cancer: According to recommendations of the American Society of Clinical Oncology/College of American Pathologists (ASCO/CAP), HER2 expression in primary BC is usually assessed by immunohistochemistry (IHC) with concluding classification into HER2 positive (IHC 3 +), HER2 equivocal (IHC 2 +), or HER2 negative (IHC 1 + or 0) [13–16].