Ewing's sarcoma/primitive neuroectodermal tumor of the prostate

Ewing’s sarcoma (ES) and primitive neuroectodermal tumor (PNET) are identified as belonging to the phenotypic spectrum of a single entity based on immunohistochemical molecular studies. ES/PNET is reported to occur in various organs; however, it rarely occurs in the prostate. We report the fifth case of a primary ES/PNET of the prostate. A 20-year-old male presented to our hospital with a history of gross hematuria and miction pain. A computed tomography (CT) scan and magnetic resonance imaging (MRI) revealed a 10.0 ¥ 7.5 ¥ 6.5 cm mass replacing the prostate gland and extending posterior to the bladder, which appeared multilobulated with intratumoral heterogeneity (Fig. 1a). The tumor was in close contact with the posterior bladder wall with possible adherence. There were multiple lung metastases in the bilateral lungs. There was no obvious lymphadenopathy or other metastases. On digital rectal examination, a firm pelvic mass was felt. The serum PSA level was 0.7 ng/mL, and all the other serum tumor markers examined (carbohydrate antigen 19-9 [CA19-9], carcinoembryonic antigen [CEA], squamous cell carcinoma related antigen [SCC], and neuron specific enolase [NSE]) were within normal limits. Histopathology of the transrectal prostate biopsy specimens showed a segmented mass of uniform small cells (Fig. 1b). The neoplastic cells exhibited diffuse, immunoreactivity for CD 99, as well as for NSE, CD56, MIB-1, and p53. The tumor cells were negative for AE1/AE3, chromogranin A, S-100, EMA, aSMA, CD34, and bcl-2. Fluorescence in situ hybridization (FISH) analysis revealed a characteristic chromosomal translocation t(11; 22) (q24; q12) for ES/PNET. On the basis of these results, the tumor was diagnosed as a primary ES/PNET of the prostate. After three cycles of chemotherapy (4.5 g ifosfamide on days 1, 2, and 3), the lung metastases had completely disappeared , and the primary lesion showed a remarkable reduction in size. The patient subsequently underwent radical prostatectomy and extended lymphadenectomy. Histopathology of the resected specimen showed areas of extensive necrosis and a small number of viable tumor cells. The surgical margins and lymph nodes were, however, free from malignant cells. He had no evidence of recurrence 10 months after surgery. A primary ES/PNET of the prostate is extremely rare, and including the present case, there have been only five case reports to date. Patient ages ranged from 20 to 31 years. Of the four patients with a description of chief complaints, miction pain or pelvic discomfort was felt in all four and dysuria in three. In all cases, the prostate gland was replaced by a large-sized tumor with extraprostatic extension. The most common CT or MRI finding was a heterogeneously enhanced mass. Occasionally, a central, non-enhancing, low-density area is seen within the mass, which may be due to the presence of hemorrhage and/or necrosis. Although the long-term prognosis has not been described , the response to chemotherapy has been good. Although primary ES/PNET of the prostate is an extremely rare soft-tissue sarcoma, it should be considered in the differential diagnosis of a prostate tumor. Several approaches, including cytogenetical methods, are important for an early, accurate diagnosis of ES/PNET.