Recently, this dichotomous classification of HER2 status has been challenged to reclassify HER2-negative breast cancer into two categories: HER2-low (IHC score of 1 + or 2 + without HER2 gene amplification) and HER2-negative (IHC score of 0, no staining [HER2-IHC 0]) breast cancer [7]. Here, ERBB2 is linked to breast cancer.