| Summary: | <i>BCOR</i> (<i>BCL6</i> corepressor)-rearranged sarcomas (BRSs) are a heterogeneous group of sarcomas previously classified as part of the group of “atypical Ewing” or “Ewing-like” sarcomas, without the prototypical <i>ESWR1</i> gene translocation. Due to their similar morphology and histopathological features, diagnosis is challenging. The most common genetic aberrations are <i>BCOR-CCNB3</i> fusion and <i>BCOR</i> internal tandem duplication (ITD). Recently, various new fusion partners of <i>BCOR</i> have been documented, such as <i>MAML3</i>, <i>ZC3H7B</i>, <i>RGAG1</i>, and <i>KMT2D</i>, further increasing the complexity of such tumor entities, although the molecular pathogenetic mechanism remains to be elucidated. Here, we present an index case of intrathoracic BRS that carried a novel <i>BCOR-CLGN</i> (calmegin) gene fusion, exhibited by a 52-year-old female diagnosed initially by immunohistochemistry due to the positivity of a BCOR stain; the fusion was identified by next-generation sequencing and was confirmed by Sanger sequencing. In silico protein analysis was performed to demonstrate the 3D structure of the chimera protein. The physicochemical properties of the fusion protein sequence were calculated using the ProtParam web-server tool. Our finding further broadens the fusion partner gene spectrum of BRS. Due to the heterogeneity, molecular ancillary tests serve as powerful tools to discover these unusual variants, and an in silico analysis of the fusion protein offers an appropriate approach toward understanding the exact pathogenesis of such a rare variant.
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