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 This evidence concerns the gene ERBB2 and breast cancer.