Mesenchymal chondrosarcoma of the head and neck with HEY1::NCOA2 fusion: A clinicopathologic and molecular study of 13 cases with emphasis on diagnostic pitfalls

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Abstract
Background: Mesenchymal chondrosarcoma (MCS) is a rare translocation‐associated sarcoma, driven by a canonical HEY1::NCOA2 fusion. The tumors typically have a biphasic phenotype of primitive small blue round cells intermixed with hyaline cartilage. The head and neck (HN) region is a common site for MCS, accounting for 12–45% of all cases reported.Aims: We assembled a relatively large cohort of 13 molecularly confirmed HN MCS for a detailed clinicopathologic analysis. The underlying fusion events were determined using fluorescence in situ hybridization and/or targeted RNA sequencing.Results: The median age of presentation was 19 years. Five MCSs (39%) had an intraosseous presentation (skull, maxilla, palate, and mandible), while the remaining eight cases occurred in the brain/meninges, orbit, and nasal cavity. Microscopically, HN MCSs were characterized by primitive round cells arranged in a distinctive nested architecture and a rich staghorn vasculature. A cartilaginous component of hyaline cartilage islands and/or single chondrocytes were present in 69% cases. A combined immunoprofile of CD99(+)/SATB2(+)/CD34(−)/STAT6(−) was typically noted. As this immunoprofile is non‐specific, the referral diagnoses in cases lacking a cartilaginous component included Ewing sarcoma family and osteosarcoma. Among the seven patients with follow‐up data, three developed distant metastasis and one died of disease.Conclusion: HN MCS may arise at intra‐ or extra‐osseous sites. The HN MCS appears to have a more prolonged survival compared other MCS sites. Testing for HEY1::NCOA2 fusion is recommended in HN tumors with nested round cell morphology and staghorn vasculature that lack a distinctive cartilaginous component.
Funding Information
  • National Institutes of Health

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