Which of the following is not true for endodermal sinus tumor

The endodermal sinus tumor (yolk sac tumor) mostly observed between 15-20 yrs of age derived from the primitive yolk sac third most frequent malignant germ cell tumors of the ovary( After Dysgerminoma, Immature teratoma) Abdominal or pelvic pain is the most frequent initial symptom, occurring in about 75% of patients, characteristic histological feature is presence of cystic spaces lined by flattened epithelium, within this space; a tuft of vascular tissue is often seen. This is ca1led as Schiller - Duval body. Surgical staging and unlateral salpingo-oopherectomy in generally the treatment of choice. tumor produces alpha feto protein which is an useful marker to monitor regression and detect recurrence.