Detection of mesenchymal chondrosarcoma in pleural effusion with immunocytochemistry and determination of HEY1::NCOA2 fusion by next-generation sequencing on cell block.

Mesenchymal chondrosarcoma (MC) is a rare but extremely aggressive type of chondrosarcoma distinguished by the presence of both primitive mesenchymal cells and fully developed chondroid tissue. The identification of a biphasic morphology in pleural effusion, along with detection of the HEY1::NCOA2 fusion using next-generation sequencing, serve as vital indicators for an accurate diagnosis.