HER2-low breast cancer

HER2-low breast cancer is an emerging HER2 status in which levels of the HER2 protein are too low to be considered HER2-positive. Currently, HER2-low breast cancers are those that have immunohistochemical (IHC) test scores of 1+ or 2+ but a negative fluorescence in situ hybridization (FISH) test. This status only has implications for patients with metastatic breast cancer and is not part of a routine pathology report.