Which of the following is not true regarding endodermal sinus tumor?

Endodermal sinus tumors (EST) are referred to as yolk sac carcinomas because they are derived from the primitive yolk sac. Abdominal or pelvic pain is the most frequent initial symptom, occurring in about 75% of patientsThe EST is unilateral in 100% of cases; thus, biopsy of the opposite ovary is contraindicated.Microscopically, the characteristic feature is the endodermal sinus or Schiller-Duval body. The cystic space is lined with a layer of flattened or irregular endothelium into which projectsa glomerulus-like tuft with a central vascular core.Most EST lesions secrete AFP and, rarely, they may elaborate detectable alpha-1 anti-trypsin (AAT). The serum level of these markers, paicularly AFP, is useful in monitoring the patient's response to treatmentThe treatment of the EST consists of surgical exploration, unilateral salpingo-oophorectomy, and a frozen section for diagnosis. The addition of a hysterectomy and contralateral salpingo-oophorectomy does not alter outcome.Ref: Berek and Novak&;s gynecology; Chapter 37; Ovarian, Fallopian Tube, and Peritoneal Cancer