In this cross-sectional study, we performed HER2/neu immunohistochemical (IHC) staining in 37 high-grade EC cases with histological diagnostic categories of PSC (n=23), clear cell carcinoma (CCC) (n=9), and carcinosarcoma with high-grade carcinomatous component (PSC, CCC, grade 3 endometrioid carcinoma, or unclassified high-grade adenocarcinoma) (n=5). The gene discussed is ERBB2; the disease is carcinosarcoma.