Ultrastructure and pathology of desmoplastic small round cell tumor

Objective To observe the change of ultrastructure and pathology of desmoplastic small round cell tumor(DSRCT)and recognize the characteristics of DSRCT and improve the standard of diagnosis.Methods One case of primary DSRCT in right leg was observed by light microscope,immunohistochemical method and electron microscope and analyzed with review of the literatures.Results The size of tumor was 3.2 cm×2.4 cm×1.3 cm with gray-yellow on cross-section.Foci of hemorrhage and necrosis were noted.Under light microscope,the tumor was composed of sharply demarcated nests of small rounded or oval cells.The cellular aggregates were surrounded and separated by abundant fibrous connective tissue.The tumor cells were uniform in size and shape,and showed small to moderate amounts of pale cytoplasm with indistinct cell borders.The nuclei were round to oval,with clumped chromatin and marked hyperchromasia.Some cells had one or two indistinct nucleoli.Numerous mitotic figures and areas of necrosis were dentified.The immunohistochemical results showed that the tumor cells were strongly positive for CK,EMA and NSE.There was focal positive staining for desmin with a perinuclear dot-like pattern.However,the tumor cells were negative for CgA,Myogenin,Syn,LCA,SMA,S-100,NF,GFAP,HMB45,HHF-35,CD3,CD10,Actin,CD99,and CD20.Under electron microscope,the tumor cells showed paranuclear cytoplasmic intermediate filaments arranging in globular or whorl array.Conclusion DSRCT occurs both in the abdomen and at other sites.The patients with DSRCT range widely in age.DSRCT has distinctive histopathologic and ultrastructural features.This tumor shows immunohistochemical feature of epithelial,mesenchymal as well as neural multidirectional differentiation.RT-PCR may be served as an important diagnostic adjunct for DSRAT.The prognosis of the patients with DSRCT is very poor.