ERBB2 and breast neoplasm: According to the standard definitions per the 2018 ASCO and College of American Pathologists guidelines [34], breast tumors with low expression of HER2, defined as immunohistochemistry (IHC)1+ or 2+ without amplification by fluorescent in situ hybridization (FISH), are considered HER2 negative and are not sensitive to standard anti-HER2 therapies.