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[Pathological features of primary extragonadal germ cell tumor of the prostate with small round blue cell morphology].

Objective: To investigate the clinicopathological features and clinical management of primary extragonadal germ cell tumor of the prostate. Methods: Two cases of primary extragonadal germ cell tumor in the prostate were collected at Fudan University Shanghai Cancer Center, in January and September 2016, respectively. Their pathological features, clinical treatments and follow-up were retrospectively analyzed. Results: The two patients were 41 and 32 years old, respectively, and both presented with obstructive symptoms of the lower urinary tract. Histologically, both cases showed small round blue cells and an invasive growth pattern. The immunohistochemistry (IHC) stains of SALL4, OCT3/4, CD117 and PLAP were all positive, while those of PSA, AR and syn were negative. Moreover, case 1 demonstrated perinuclear dot-like staining for CKpan, which might be a diagnostic pitfall. There was no evidence of disease in other areas via physical examination or radiographic studies. Based on these IHC findings and the morphology, the two cases were diagnosed as primary seminoma of the prostate, which were consequently treated with six cycles of bleomycin, etoposide and cisplatin-based chemotherapy. A complete response was achieved in case 1. Case 2 was followed up and showed tumor recurrence, and progression with elevated tumor marker AFP. The subsequent radical removed specimens of case 2 were finally diagnosed as mixed germ cell tumor of the prostate. Conclusion: As a rare neoplastic entity, primary germ cell tumor of the prostate can show small blue round cell morphology. Pathologically, the morphology of small round blue cells combined with a perinuclear dot-like pattern of CKpan IHC staining may be a diagnostic pitfall. The clinical treatment strategy should be evaluated with consideration of the pathological diagnosis and comprehensive evaluation of the tumor markers.