ERBB2 and neoplasm: According to the ASCO/CAP guidelines [3], HER2 IHC scoring is defined as follows: HER2 0+ indicates either no observed staining or incomplete membrane staining that is faint/barely perceptible in <10% of invasive tumor cells, HER2 1+ indicates incomplete faint perceptible membrane staining within >10% of invasive tumor cells, HER2 2+ indicates weak to moderate complete membrane staining observed in >10% of invasive tumor cells, and HER2 3+ indicates complete, intense circumferential membranous staining in >10% of invasive tumor cells.