[Extraskeletal mesenchymal chondrosarcoma in central nerve system: a clinicopathological analysis].

Objective: To investigate the clinicopathological features, immunophenotype, molecular genetics and prognosis of extraskeletal mesenchymal chondrosarcoma in central nerve system (CNS). Methods: The clinicopathological findings, immunohistochemistry and genetic analysis of four cases of extraskeletal mesenchymal chondrosarcoma in Xuanwu Hospital between 2014 and 2019 were reviewed and followed up. Results: The ages of patients ranged from 20-35 years. Three patients had intracranial lesions and one had intradural tumor. The characteristic histologic features were undifferentiated small cells together with scattered islands of hyaline cartilage. There was hemangiopericytoma-like pattern with calcification and ossification. The tumor cells were positive for VIM and SOX9; and the small cells were positive for CD99, NSE and NKX3.1. The cells in chondroid matrix were positive for S-100. All tumor cells were negative for markers including CKpan, EMA and desmin. At molecular analysis, HEY1-NCOA2 fusion transcripts were identified in three patients. The fusion points were between exon 4 of HEY1 and exon 13 of NCOA2. Follow-up information was obtained in two patients, and both were free from recurrence or metastasis at 8 and 20 months. Conclusions: Extraskeletal mesenchymaI chondrosarcoma is a rare CNS disease with poor prognosis. In addition to SOX9, NKX3.1 can be another useful antibody for the differential diagnosis. The combination of pathological characteristics, immunophenotype and genetic profile of tumor is essential for diagnosis.