EFO_1000358 (Malignant Ovarian Mixed Epithelial Tumor) can be described as follows. A malignant epithelial tumor arising from the ovary. It is characterized by an admixture of two or more of the five major cell types: serous, mucinous, endometrioid, clear, and Brenner/transitional. The second or second and third cell types must comprise alone or together at least 10% of the tumor epithelium, or, in the case of a mixed Brenner-mucinous cystic tumor, both components should be macroscopically visible. The least differentiated component determines the tumor grade (WHO, 2003).