ERBB2 and breast cancer: In the pivotal phase 2 single-agent and phase 3 combination studies of trastuzumab against breast cancer [8,32], the IHC scoring system was more organized in relation to the HER2 receptor number (no staining (score 0), <20,000 receptors; partial membrane staining with <10% of the cells showing complete membrane staining (score 1+), 100,000 receptors; light to moderate complete membrane staining in >10% of the cells (score 2+), 500,000 receptors; and complete membrane staining in >10% of the cells (score 3+), 2,300,000 receptors) [33].