133 Primary Prostatic Pure Yolk Sac Tumor

Abstract Objectives Extragonadal yolk sac tumor (YST) is a rare malignant neoplasm that usually arises in mediastinal, sacrococcygeal, retroperitoneal and head and neck regions. Only seven cases of primary prostatic YST have been reported in the literature. We report a case of prostatic YST in a young adult. Methods A 26-year-old man was admitted with a history of urinary urgency, hematuria, hematochezia, and pelvic pain. Abdominal and pelvic CT/MRI scans showed a 12.0 x 11.0 x 9.1 cm prostatic mass locally invading the rectum and bladder neck with lymphadenopathy and hepatic metastases. No testicular lesion was identified by physical exam or sonography. An initial liver biopsy showed a high-grade round cell tumor. The immunohistochemical staining pattern was suspicious for Ewing sarcoma. Transrectal ultrasound-guided prostatic biopsy was performed for definitive evaluation. Results The tumor exhibited an admixture of glandular, cord-like, solid, and papillary architectures. Occasional capillaries surfaced by a double layer of tumor cells resembling primitive glomeruli were present (Schiller-Duval bodies). Immunohistochemical stains were positive for AE1/3, SALL4, CDX2, and AFP (focal), and were negative for OCT3/4, CD30, C-kit, inhibin, hCG, CK7, CK20, PLAP, PAS, PSAP, and NKX3.1. The histologic and immunohistochemical findings were diagnostic of extragonadal YST. The patient responded well to four courses of etoposide, isophosphamide and cisplatin chemotherapy, with marked shrinkage of the primary and metastatic tumors. Serum AFP decreased from a pretreatment baseline of 7,207 to 7 IU/mL. Conclusion Extragonadal YST of the prostate is a very rare tumor that poses a diagnostic challenge due to its anatomic location and diverse histological patterns. A high index of suspicion and appropriate immunohistochemical studies facilitate an accurate diagnosis.