ERBB2 and neoplasm: Notably, the 2023 ASCO/CAP guidelines for HER2 testing in EC, largely in line with ISGyP, define IHC 3+ as intense complete or basolateral/lateral membrane staining in >30% of tumor cells; 2+ as intense complete or basolateral/lateral membrane staining in <30%, or weak to moderate staining in ≥10% of tumor cells; 1+ as incomplete membrane staining that is faint/barely perceptible in any proportion of cells or weak complete staining in <10% of tumor cells; and 0 as no staining [29].