primitive neuroectodermal tumor ( pnet ) is a member of the ewing 's sarcoma family of tumors ( esft ) and has a common chromosomal translocation found in ewing 's sarcomas . , we describe a case of renal pnet that was finally diagnosed by fluorescence in situ hybridization ( fish ) and transmission electron microscopy ( tem ) . it was responsive to preoperative vdc - ie ( combined vincristine , doxorubicin and cyclophosphamide followed by another combination of ifosfamide and etoposide ) chemotherapy and was subjected to surgical treatment . the patient was a 66-year - old male who visited our hospital with asymptomatic gross hematuria . enhanced computed tomography ( ct ) , magnetic resonance imaging and bone scintigraphy were performed , and a large solid tumor was found within the parenchyma of the middle pole of the left kidney ( fig . the serum level of neuron - specific enolase ( nse ) was 110 ng / ml ( normal range 012 ng / ml ) . since the tumor showed no indication of an early enhancement and early washout , it was suspected to be a nonrenal cell carcinoma such as urothelial carcinoma or soft tissue sarcoma . therefore , a fine - needle biopsy of the left renal tumor was performed and showed a small round cell tumor in the hematoxylin - eosin staining ( fig . three courses of vdc - ie chemotherapy were applied , and the left renal tumor showed a partial response . . therefore , left radical nephrectomy and adrenalectomy were performed . after surgery , external beam radiation was performed on the metastatic lesion of the right ischium . the fine - needle biopsy specimen showed a small round cell tumor on the hematoxylin - eosin staining ( fig . 1c ) , nse and synaptophysin were positive , and ck7 , ck20 , ae1/ae3 ( fig . 1e ) , sma , cd45 ( fig . 1f ) and wt-1 were negative . thus , this tumor was initially suspected to be in esft . on gross examination of the resected tumor ( fig . 2a ) , the primary tumor mass in the middle pole of the left kidney measured 4 cm in maximum diameter and showed invasion toward the surrounding adipose tissue . on the cut surface , histopathological tests of the resected tumor showed atypical bare nuclear round cells with scant cytoplasm ( fig . 2d ) and nse , and negative for ck7 , ck20 , desmin and sma . cellular proliferation , as evaluated by ki-67 expression in the resected specimen was lower than in the biopsy specimen because of the efficacy of preoperative vdc - ie chemotherapy ( fig . 2e , f ) . for the differential diagnosis of other small round cell tumors such as small - cell carcinoma , fish for the ewsr1 gene was performed . one pair of signals split apart due to rearrangement of the ewsr1 gene was detected ( fig . 3a ) , supporting the diagnosis of this tumor in the esft . for the differential diagnosis between pnet and ewing 's sarcoma , this enabled us to determine the final diagnosis of this tumor to be a pnet . for assessment of the therapeutic options , we assessed the expression of c - kit , pdgfr and vegf as known growth factors in tumor proliferation . ewing 's sarcoma and pnet form a single group of bone and soft - tissue tumors called esft with typical undifferentiated ewing 's sarcoma at one end of the spectrum and pnet with clear evidence of neural differentiation at the other . pnets are derived from primitive neural crest cells and are usually found in bone or soft tissues of the extremities , trunk , head and neck , and less commonly in the viscera or kidneys [ 3 , 4 , 5 ] . no specific signs of pnet have been described on ultrasonography , ct or magnetic resonance imaging . the typical histological features of renal pnet are monotonous proliferation of immature and small round cells and formation in some rosettes of the homer - wright or flexner types . immunohistochemical analysis shows high positivity for nse and cd99 , but these are not entirely specific . in some cases , positivity for vimentin and cytokeratin has been detected [ 1 , 6 , 7 ] . it is sometimes difficult to distinguish pnet from other small round cell tumors that localize to the kidney such as small - cell carcinoma , desmoplastic small round cell tumor , neuroblastoma , malignant lymphoma , synovial sarcoma and wilms tumor . this is because of the considerable morphological similarity between these tumors as well as the rarity of pnet . another important criterion is cytoplasmic dense - core membrane - bound neurosecretory granules , a few organelles , and poorly developed cell junctions demonstrated by ultrastructural methods . ewing 's sarcoma and pnet have a common chromosomal translocation t(11;22)(q24;q12 ) , which leads to the formation of the ewl / fli-1 fusion protein . finally , the gold standard for the diagnosis is to confirm the characteristic translocation by a molecular biological technique such as fish to detect ewsr1 gene split signals [ 9 , 10 ] . in this case , one pair of signals split apart due to rearrangement of the ewsr1 gene was detected , suggesting the diagnosis of this tumor in esft . for the differential diagnosis of pnet from esft , tem was performed , and neuroendocrine granules and microtubules were observed as the features of pnet , and the diagnosis of this tumor was finalized . a standard treatment for advanced renal pnet has not been established because of the rarity of the disease . the recommended treatment for extraosseous esft is with similar regimens as esft of bone . standard chemotherapy for esft was performed with vdc and actinomycin d alternating with ie [ 11 , 12 ] . in this case , vdc - ie was effective and achieved a partial response , and a left nephrectomy was performed . however , because metastatic esft relapses at a high rate , another therapeutic option is needed . in a few reports about preoperative chemotherapy for esft , the histological response to preoperative chemotherapy was the important predictor of event - free survival . in this case , preoperative chemotherapy was effective according to the ki-67 immunohistochemistry test . the expressions of growth factors such as pdgfr , vegf and c - kit in esft and the effectiveness of tyrosine kinase inhibitors targeted to such growth factors have been reported sporadically [ 14 , 15 ] . therefore , an immunohistochemical analysis was performed for the expression of pdgfr , c - kit and vegf . some tyrosine kinase inhibitors are known to inhibit pdgfr or c - kit such as pazopanib , imatinib and sunitinib . bone marrow hypoplasia developed in this patient as a result of repetitive vdc - ie chemotherapy after surgery . consequently , tyrosine kinase inhibitor remains as a potent therapeutic option for this patient . in summary , we reported a case of renal pnet in which fish contributed to the final diagnosis . pnet has a poor prognosis , but tyrosine kinase inhibitor offers promise as a potential therapeutic agent in the future .
primitive neuroectodermal tumor ( pnet ) is a member of the ewing 's sarcoma family of tumors ( esft ) . 
 we report a case of pnet in a 66-year - old male who presented with a large solid tumor within the parenchyma of the middle pole of the left kidney with metastases to the left adrenal gland and right ischium . a fine - needle biopsy was performed and showed a small round cell tumor . 
 results of immunohistochemical staining suggested this tumor belonged to esft . 
 preoperative vdc - ie ( combined vincristine , doxorubicin and cyclophosphamide followed by another combination of ifosfamide and etoposide ) chemotherapy and left radical nephrectomy and adrenalectomy were performed . 
 the histopathological findings of the resected tumor were similar to those in the biopsy specimen , but the results of ae1/ae3 were different . 
 for the diagnosis , fluorescence in situ hybridization was performed . 
 split signals of the ewsr1 gene were detected , and transmission electron microscopy showed neuroendocrine granules and microtubules . 
 the final diagnosis of this tumor was pnet of the kidney .