Not a germ cell tumor of ovary:

Germ cell tumors (GCT) account for 15-20% of ovarian tumors and the vast majority (95%) are benign cystic teratomas. The remaining 5% are found principally in children and young adults and have a higher incidence of malignant behavior various germ cell tumors are as under: Mature (benign) teratomas Immature (malignant) teratomas Monodermal or highly specialized teratomas          Dysgenninomas Endodermal (yolk) sac tumors Choriocarcinoma Embryonal carcinoma   Polyembryoma Mixed germ cell tumors (MGCT) Brenner tumors are uncommon tumors which account for less than 2% of ovarian neoplasms. These solid neoplasms are characterized by a dense fibrous stroma "punctuated" by nests of transitional cells resembling those lining the urinary bladder. Brenner tumors are occasionally found in mucinous cyst adenomas suggesting that these tumors arise from coelomic epithelial inclusion cysts through metaplasia of the cyst lining of transitional epithelium.