{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,3,5]],"date-time":"2026-03-05T07:53:45Z","timestamp":1772697225809,"version":"3.50.1"},"reference-count":22,"publisher":"Frontiers Media SA","license":[{"start":{"date-parts":[[2026,3,5]],"date-time":"2026-03-05T00:00:00Z","timestamp":1772668800000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":["frontiersin.org"],"crossmark-restriction":true},"short-container-title":["Front. Pediatr."],"abstract":"<jats:sec>\n                    <jats:title>Background<\/jats:title>\n                    <jats:p>\n                      Mesenchymal chondrosarcoma (MCS) is a rare and highly aggressive subtype of chondrosarcoma, accounting for less than 1% of all chondrosarcomas. It predominantly affects adolescents and young adults and frequently arises in craniofacial bones and soft tissues. Diagnosis is challenging because of significant histological overlap with other high-grade spindle cell sarcomas, particularly when the cartilaginous component is minimal or absent. The identification of the\n                      <jats:italic>HEY1::NCOA2<\/jats:italic>\n                      gene fusion has emerged as a highly specific molecular marker for MCS, substantially improving diagnostic accuracy and providing potential therapeutic implications.\n                    <\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Case presentation<\/jats:title>\n                    <jats:p>\n                      We report the case of a 13-year-old girl who presented with a 3-month history of progressive right cheek swelling. Imaging revealed a destructive mass in the right maxillary sinus. Histopathological evaluation demonstrated a high-grade spindle cell tumor, initially interpreted as fibrosarcoma, showing diffuse vimentin positivity, a high Ki-67 proliferation index (35%\u201340%), and CD34 negativity. Comprehensive molecular analysis confirmed a pathogenic\n                      <jats:italic>HEY1::NCOA2<\/jats:italic>\n                      gene fusion, while ETV6::NTRK3 fusion was excluded. The patient was treated with VAC chemotherapy (vincristine, actinomycin D, cyclophosphamide), local radiotherapy (60\u2005Gy), cranial prophylactic radiotherapy (12\u2005Gy), and subsequent debulking surgery. Follow-up\n                      <jats:sup>18<\/jats:sup>\n                      F-FDG PET\/CT demonstrated a partial metabolic response. Given persistent disease and molecular evidence suggesting activation of the PI3K\/AKT\/mTOR pathway in MCS, maintenance therapy with the mTOR inhibitor sirolimus was initiated.\n                    <\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Conclusion<\/jats:title>\n                    <jats:p>\n                      This case highlights the pivotal role of molecular diagnostics\u2014particularly RNA sequencing\u2014in establishing the diagnosis of mesenchymal chondrosarcoma and differentiating it from other high-grade pediatric sarcomas with overlapping morphology. Identification of the\n                      <jats:italic>HEY1::NCOA2<\/jats:italic>\n                      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\n                      <jats:italic>HEY1::NCOA2<\/jats:italic>\n                      fusion managed with sirolimus-based maintenance therapy.\n                    <\/jats:p>\n                  <\/jats:sec>","DOI":"10.3389\/fped.2026.1758538","type":"journal-article","created":{"date-parts":[[2026,3,5]],"date-time":"2026-03-05T06:54:53Z","timestamp":1772693693000},"update-policy":"https:\/\/doi.org\/10.3389\/crossmark-policy","source":"Crossref","is-referenced-by-count":0,"title":["Maxillary mesenchymal chondrosarcoma harboring HEY1::NCOA2 fusion in a 13-year-old girl: a rare case report and literature review"],"prefix":"10.3389","volume":"14","author":[{"given":"\u015eule","family":"\u00c7al\u0131\u015fkan Kam\u0131\u015f","sequence":"first","affiliation":[{"name":"Department of Pediatric Hematology and Oncology, Adana Faculty of Medicine, Adana City Training and Research Hospital, University of Health Sciences","place":["Adana, T\u00fcrkiye"]}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Beg\u00fcl","family":"Ya\u011fc\u0131","sequence":"additional","affiliation":[{"name":"Department of Pediatric Hematology and Oncology, Adana Faculty of Medicine, Adana City Training and Research Hospital, University of Health Sciences","place":["Adana, T\u00fcrkiye"]}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Ay\u015fe Selcan","family":"Ko\u00e7","sequence":"additional","affiliation":[{"name":"Department of Pediatric Radiology, Adana Faculty of Medicine, Adana City Training and Research Hospital, University of Health Sciences","place":["Adana, T\u00fcrkiye"]}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"G\u00fcliz","family":"Durak","sequence":"additional","affiliation":[{"name":"Department of Nuclear Medicine, Adana Faculty of Medicine, Adana City Training and Research Hospital, University of Health Sciences","place":["Adana, T\u00fcrkiye"]}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Ali","family":"Yitik","sequence":"additional","affiliation":[{"name":"Department of Pathology, Adana Faculty of Medicine, Adana City Training and Research Hospital, University of Health Sciences","place":["Adana, T\u00fcrkiye"]}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1965","published-online":{"date-parts":[[2026,3,5]]},"reference":[{"key":"B1","doi-asserted-by":"publisher","first-page":"e160279","DOI":"10.1172\/jci.insight.160279","article-title":"HEY1-NCOA2 Expression modulates chondrogenic differentiation and induces mesenchymal chondrosarcoma in mice","volume":"8","author":"Tanaka","year":"2023","journal-title":"JCI Insight"},{"key":"B2","doi-asserted-by":"publisher","first-page":"579","DOI":"10.1002\/path.5899","article-title":"Genomic profiling identifies genes and pathways dysregulated by HEY1-NCOA2 fusion and shines a light on mesenchymal chondrosarcoma tumorigenesis","volume":"257","author":"Qi","year":"2022","journal-title":"J Pathol"},{"key":"B3","doi-asserted-by":"publisher","first-page":"258","DOI":"10.1186\/s12886-025-04082-z","article-title":"Orbital mesenchymal chondrosarcoma and its specific fusion gene HEY1-NCOA2","volume":"25","author":"Lin","year":"2025","journal-title":"BMC Ophthalmol"},{"key":"B4","doi-asserted-by":"publisher","first-page":"e228969","DOI":"10.1136\/bcr-2018-228969","article-title":"Mesenchymal chondrosarcoma of maxilla in paediatric patient","volume":"12","author":"Choo","year":"2019","journal-title":"BMJ Case Rep"},{"key":"B5","doi-asserted-by":"publisher","first-page":"37","DOI":"10.1007\/s11912-018-0668-z","article-title":"Mesenchymal chondrosarcoma: a review with emphasis on its fusion-driven biology","volume":"20","author":"Beaino M","year":"2018","journal-title":"Curr Oncol Rep"},{"key":"B6","doi-asserted-by":"publisher","first-page":"127","DOI":"10.1002\/gcc.20937","article-title":"Identification of a novel, recurrent HEY1-NCOA2 fusion in mesenchymal chondrosarcoma based on a genome-wide screen of exon-level expression data","volume":"51","author":"Wang","year":"2012","journal-title":"Genes Chromosomes Cancer"},{"key":"B7","doi-asserted-by":"publisher","first-page":"4581","DOI":"10.3390\/cancers15184581","article-title":"Mesenchymal chondrosarcoma from diagnosis to clinical trials","volume":"15","author":"Dudzisz-\u015aled\u017a","year":"2023","journal-title":"Cancers (Basel)"},{"key":"B8","doi-asserted-by":"publisher","first-page":"2723","DOI":"10.1007\/s00381-024-06452-2","article-title":"Extra-skeletal intracranial mesenchymal chondrosarcoma: systematic literature review","volume":"40","author":"Kumarasamy","year":"2024","journal-title":"Childs Nerv Syst"},{"key":"B9","doi-asserted-by":"publisher","first-page":"374","DOI":"10.1016\/j.ejca.2014.11.007","article-title":"Mesenchymal chondrosarcoma: prognostic factors and outcome in 113 patients. 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