ERBB2 and breast cancer: It could be hypothesized that even a lower number of HER2 molecules on the breast cancer cell membrane (100,000 to 500,000 HER2 molecules on the cell membrane of score 1 + and 2 + breast cancer cells versus over two million on score 3 + cells) [71, 72] could be enough to elicit an effective NK cell-mediated ADCC.