Desmoplastic small round cell tumor with atypical immunohistochemical profile and rhabdoid-like differentiation

摘要

Desmoplastic small round cell tumor(DSRCT)is a rare,aggressive malignant neoplasm of unknown origin,and is comprised of small round cells with a characteristic desmoplastic stroma.DSRCT typically expresses epithelial,mesenchymal and neural markers simultaneously.We describe a case of DSRCT with an atypical immunohistochemical profile and rhabdoid-like tumor cells on electron microscopy.In the present case,the neoplastic cells were positive only for vimentin,desmin(cytoplasmic membranous pattern)and CD56,and negative for smooth muscle actin,synaptophysin,CD117,CD45,myogenin,CAM5.2,pancytokeratin,WT1,EMA,CD99,neurofilament,CD34 and p53.Ki67 showed a low proliferative activity.Electron microscopy showed focal rhabdoid differentiation.However,INI-1(SNF-5/BAF47)demonstrated preservation of nuclear positivity in the neoplastic cells.Cytogenetic studies showed translocation t(11;22)(p13;q12)confirming an EWSR1-WT1 translocation characteristic for DSRCT,and t(1;15)(q11;p11.2)of unknown significance.This case is a diagnostic challenge because of atypical immunohistochemical profile and cytogenetic study is crucial in rendering the correct diagnosis.