A Study Of Peripheral Primitive Neuroectodermal Tumor On Its Clinical Pathology And Molecular Biology

Peripheral primitive neuroectodermal tumor(PNET) is a highly malignant primary tumor of bone and soft tissues, with a marked propensity for dissemination, mainly affecting adolescents and young adults. Histologically, PNET is characterized by poorly differentiated cells with uniform nuclei and scanty cytoplasms, unfortunately always confused with other poorly differentiated small round cell tumors, making the diagnosis sometime tremendously difficult just by conventional light microscopy. So the use of immunohistochemistry is valuable and the positive of CD99 antibodie provides strong support for PNET. However, CD99 expression later was also found on several unrelated types of tumors, such as lymphoblastic lymphoma, rhabdomyosarcoma, myeloblastoma. Thus limits its reliability and requires us to reread its value. Cytogenics studies have found characteristic chromosome translocations in overwhelming majority of PNET cases, resulting in a fusion gene, composed of the 5' portion of EWS gene at 22ql2 and the 3' portion of a member of the ETS family oftranscription factors. Further study documented that the fusion gene plays an important role in the oncogenesis of PNET by activating some target genes as an aberrant transcription factor. Moreover, the fusion gene has several alternative forms according to the variation in the precise breakpoint location, and the different forms possess different transcriptional activation and outcome with different clinical behavior of the tumor, perhaps correlating to the outcomes of the patients.In this study, we investigated the histopathological, immunohistochemical and molecular genetic features of PNET, evaluated the expression of some specific antibodies and detected EWS-FLI1 fusion gene by nested reverse transcription polymerase chain reaction(RT-PCR). Thus, their value in the diagnosis, differential diagnosis and prognostic evaluation of PNET were assessed, and the oncogenic function of the fusion gene was also primarily discussed.Materials and Methods:Sixty cases of small round cell tumor were collected from the archives, including 35 PNETs, 10 malignant lymphomas, 2 neuroblastomas, 4 rhabdomyosarcomas, 3 small cell neuroendocrine carcinomas, 3 small cell malignant melanomas and 3 poorly differential synovial sarcomas. Antibodies of CD99, Syn, CgA, S-100, Vim, EMA, Des, PCNA, C-myc and Cyclin-D1 were performed by SPimmunohistochmical methods and EWS-FLI1 fusion gene were detected by RT-PCR.Results:Immunohistochemically, among 35 cases of PNET, 32 were strongly positive for CD99(91.4%), 13 for Syn(37.1%), 7 for CgA(20%), 8 for S-100(22.9%), 22 for Vim(68.6%), 4 for EMA(11.4%) and none positive for Desmin. CD99 was higher expressed than any other marker in statistics. Markers for mesenchymal and neural differentiation were much higher than those for epithelia and myogenic differentiation.Among the 12 PNET cases in this study, RNA was successfully isolated in 9 cases. EWS-FLI1 fusion transcripts were detected in 6 out of 9 cases(66.7%) by nested RT-PCR. No EWS-FLI1 fusion transcripts were found in non-PNET tumors, though RNA was successfully extracted.Conclusion:1. According to the histopathological and immunohistochemical observation of PNET and other small round cell tumors, we concluded that the diagnostic criteria of PNET should composed by clinical data, histomorphologic features, immunohistochemical results and molecular detection.2. It is applicable to detect EWS-FLI1 fusion gene in formalin-fixed...