Primary primitive neuroectodermal tumor of the kidney: A case report Suna Erkılıc¸ 1 , Cos¸kun O ¨ zsarac¸ 1 , N. Emrah Koc¸er 2 & Ahmet Erbag˘cı 3 1 Department of Pathology, Faculty of Medicine, Gaziantep University, Gaziantep, Turkey; 2 Department of Pathology, Faculty of Medicine, Baskent University, Adana Teaching and Medical Research Center, Adana, Turkey; 3 Department of Urology, Faculty of Medicine, Gaziantep University, Gaziantep, Turkey Abstract. There are nearly 50 PNET cases in the literature with primary renal localization. The mean age for renal PNET is 28 but it can be seen in a wide range between 4 and 69 years. In this atypical localization PNET may be mistaken with a variety of small round cell tumors, particularly with blastema predominant Wilms’ tumor and due to its distinctive prognostic and therapeutic features differential diagnosis is very important. Immunohistochemical studies are useful in discriminating PNET from other renal small round cell tumors. Renal PNETs tend to metastasize at early stages and they have a high rate of recurrence. Our case is a 45-year-old male presented with left flank pain and hematuria. In computerized tomography a mass in left kidney was observed and nephrectomy was performed. Histopathologic examination revealed a small round cell tumor with rosettes and pseudorosettes. Immunohistochemically the lesion was diffuse strong positive with CD99 and NSE, negative with LCA, pancytokeratin, vimentin, desmin, smooth muscle actin, chromogranine A and S-100. At the time of diagnosis the pathologic stage of the tumor was T1aN0Mx. The patient did not take any further therapy and in 1-year follow-up no local recurrence or distant metastasize occurred. Key words: Ewing sarcoma, Kidney, Primitive neuroectodermal tumor (PNET), Small round cell tumor Introduction Besides its common tumors a variety of ‘‘round cell’’ tumors, including lymphoma, neuroblastoma, small cell carcinoma, clear cell sarcoma, mono- phasic synovial sarcoma, desmoplastic round cell tumor, blastema predominant Wilms’ tumor (WT), and extraskeletal Ewing’s sarcoma (EWS)/primitive neuroectodermal tumor (PNET) may be seen in kidney. Because of their different prognostic and therapeutic features, differential diagnosis of the renal round cell tumors is essential. PNET with a primary renal localization is extraordinarily rare. There are nearly 50 cases in literature, and most of them are children or ado- lescents. There is a high recurrence rate and a tendency to metastasizing to regional lymph nodes, lungs, liver, bone and bone marrow at early stages. It carries the ominous prognostic characteristics of the PNETs of all sites [1]. Herein, we reported an additional case of primary PNET in kidney. Case report Fourty-five-year-old male patient was admitted to the hospital with a left flank pain and hematuria. Ultrasonography and abdominal CT revealed a mass in mid-upper portion of the left kidney 5 cm in diameter (Figure 1). Left radical nephrectomy performed with a presumptive diagnosis of renal cell carcinoma. Macroscopically, the specimen was 11 Â 8 Â 6 cm. In cut surface there was a gray-brown lesion with a greatest diameter of 5 cm, localized in the mid-upper part of kidney. It was containing small hemorrhagic focuses. International Urology and Nephrology (2006) 38:199–202 Ó Springer 2006 DOI 10.1007/s11255-006-6675-2