ERBB2 and ovarian cancer: However, the role of HER2 in ovarian cancer is less clear.3 HER2 is more frequently expressed in OCCC (43%) than in other ovarian cancer subtypes such as serous (21%), ovarian endometrioid (23%), and mucinous (30%).4 When OCCC cell lines and xenograft models were treated with trastuzumab, it exhibited dose-dependent inhibition that correlates with HER2 expression.4