Maxillary mesenchymal chondrosarcoma harboring HEY1::NCOA2 fusion in a 13-year-old girl: a rare case report and literature review

This case highlights the pivotal role of molecular diagnostics-particularly RNA sequencing-in establishing the diagnosis of mesenchymal chondrosarcoma and differentiating it from other high-grade pediatric sarcomas with overlapping morphology. Identification of the <i>HEY1::NCOA2</i> fusion not only confirms the diagnosis but may also support biologically targeted therapeutic strategies. Multimodal treatment incorporating chemotherapy, radiotherapy, surgery, and targeted maintenance therapy can achieve meaningful disease control in aggressive craniofacial MCS. To our knowledge, this represents one of the very few reported pediatric cases of maxillary MCS with confirmed <i>HEY1::NCOA2</i> fusion managed with sirolimus-based maintenance therapy.