Final Diagnosis -- Yolk sac tumor


FINAL DIAGNOSIS: Yolk sac tumor arising in association with mature cystic teratoma (dermoid cyst).

DISCUSSION:

Yolk sac tumor (also known as endodermal sinus tumor) of the ovary is a malignant germ cell neoplasm. It often occurs in pure form but is also frequently found as a component of mixed malignant germ cell tumors. Yolk sac tumor occurs at a median age of 18 years and is nearly as common as dysgerminoma in young patients. A typical presentation is abdominal pain and a large, unilateral, rapidly growing pelvic mass. In about 10% of patients, rupture or torsion of the tumor occurs. Greatly increased serum levels of -fetoprotein (> 1000 ng/ml) are consistently found in patients with yolk sac tumor, whether pure or as a component of a mixed germ cell tumor; other ovarian tumors (i.e., immature teratoma, Sertoli-Leydig cell tumor) may also be associated with increased -fetoprotein, but usually at lower levels than those seen in patients with yolk sac tumor.

At gross evaluation, yolk sac tumors are large (average diameter 15 cm) and encapsulated with a smooth, glistening external surface. Characteristically, the sectioned surface is solid and cystic with soft, gray-to-yellow tissue and areas of hemorrhage and necrosis. A concomitant benign mature teratoma (dermoid cyst) is frequently seen.

The most common ("typical") pattern consists of papillary projections, each of which contains a central blood vessel, surrounded by a thick layer of basement membrane material, and then covered by a layer of embryonic epithelial cells with clear or eosinophilic cytoplasm; this structure is referred to as a Schiller-Duval body. Another frequently encountered feature is hyaline globules, which are eosinophilic, PAS-positive, diastase-resistant globules.

Yolk sac tumors display a variety of histologic patterns. Most will contain areas of the typical pattern, but tumors consisting purely of a histologic variant have been reported. Recognition of other patterns is important, because the differential diagnosis varies between patterns, and some patterns are reported to be more resistant to chemotherapy. Some of these patterns and their differential diagnoses are listed in the table below.


Yolk sac tumors are typically diffusely positive with immunohistochemical stains for -fetoprotein (AFP) placental alkaline phosphatase (PLAP), -1 antitrypsin, and cytokeratin. Epithelial membrane antigen (EMA) and human chorionic gonadotropin (hCG) are usually negative. The hyaline globules are positive for PAS-D and negative for -1 antitrypsin. Finally, the thick basement membrane material within papillary structures is positive for laminin and type IV collagen. The combination of the morphologic findings (Schiller-Duval bodies, hyaline globules) and positivity for AFP and cytokeratin are useful in separating yolk sac tumor from other entities in the differential diagnosis.

REFERENCES:

  1. Roth LM. Variants of yolk sac tumor. Pathol Case Rev 2005; 10 (4): 186-192.
  2. Roth LM, Talerman A. Recent advances in the pathology and classification of ovarian germ cell tumors. Int J Gynecol Pathol 2006; 25 (4): 305-320.
  3. Dabbs DJ, ed. Diagnostic Immunohistochemistry, 2nd ed. Elsevier: Philadelphia, 2006.
  4. Kumar V, Abbas AK, Fausto N, eds. Robbins and Cotran Pathologic Basis of Disease, 7th ed. Elsevier: Philadelphia, 2004.
  5. Tavassoli FA, Devilee P, eds. World Health Organization Classification of Tumours. Pathology and Genetics of Tumours of the Breast and Female Genital Organs. IARC Press: Lyon, 2003.
  6. Kurman RJ, ed. Blaustein's Pathology of the Female Genital Tract, 5th ed. Springer-Verlag: New York, 2002.
  7. Prat J. Pathology of the Ovary. Elsevier: Philadelphia, 2004.
  8. Rosai J. Rosai and Ackerman's Surgical Pathology, 9th ed. Elsevier: Philadelphia, 2004.
  9. Silverberg SG, DeLellis RA, Frable WJ. Silverberg's Principles and Practice of Surgical Pathology and Cytopathology. Elsevier: Philadelphia, 2006.

Contributed by J. Manuel Zarandona, M.D., and Mamatha Chivukula, M.D.




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