Diagnosis: Yolk Sac Tumor
• An elevated AFP level in a young woman most frequently suggests a yolk sac tumor or yolk cell components in a mixed germ cell tumor. However, there are pitfalls. AFP elevations have been reported in Sertoli-Leydig cell tumors without yolk sac elements.
• The best-known feature of yolk sac tumor is Schiller-Duval body. Schiller-Duval bodies resemble the endodermal sinus of rat placenta. It was originally thought that these lesions were seen in approximately 75% of yolk sac tumors. However, it is now known that Schiller-Duval bodies are seen in only a few of these tumors.
• The differential diagnosis for yolk sac tumor includes Sertoli-Leydig cell tumor and juvenile granulosa cell tumor, both of which occur in young women. These tumors stain for inhibin, which is negative in yolk sac tumor.
• Clear cell carcinoma may cause diagnostic difficulty in assessing a yolk sac tumor, although the former is much more common in older women. However, immunohistochemistry is useful in differentiating these two neoplasms. Yolk sac tumors are almost uniformly positive for AFP. Clear cell carcinomas of the ovary are negative for AFP but tend to be positive for cytokeratin 7, CAM 5.2, 34βE12, carcinoembryonic antigen (CEA), Leu-M1, vimentin, BCL2, p53, and CA 125. Clear cell carcinomas are variably positive for ER and Her2.
• Yolk sac tumors also must be differentiated from other germ cell tumors. Yolk sac tumors most closely resemble embryonal carcinoma, although embryonal carcinomas are more pleomorphic and lack the patterns of yolk sac tumor.