ERBB2 and endometrial serous adenocarcinoma: For example, in uterine serous carcinoma (USC), a biologically aggressive endometrial tumor, whole exome sequencing (WES) and confirmatory IHC studies revealed that up to 35% of cases harbor human epidermal growth factor receptor 2 (HER2) overexpression, and over 50% of patients overexpressing HER2 at 3 + levels demonstrated high heterogeneity (at least two-degree difference in staining intensity involving tumor cells)16,21.