ERBB2 and breast carcinoma: The success experiences of trastuzumab therapy in breast cancer, gastric, or gastroesophageal junction (GEJ) cancer patients and newly developed anti-HER2 drugs encouraged the investigation of anti-HER2 therapy application in other cancers, including mucinous EOC.10,11 However, there is, so far, no consensus in defining the HER2 positivity in mucinous EOC.12