BCOR-ITD Rearranged Sarcoma in the Mandible of a 5-Year-Old Child: A Case Report Highlighting Diagnostic Distinction From Odontogenic Fibromyxoma

The 5th edition of the World Health Organization (WHO) classification of soft tissue and bone has recognized three distinct groups among Ewing-like sarcomas, namely, CIC-rearranged sarcoma, sarcomas with <i>BCOR</i> genetic alterations, and round cell sarcomas with EWSR1:: non-ETS fusions. Sarcomas with <i>BCOR</i> genetic alterations are a distinct clinicopathological group of high-grade tumors, representing 5% of small round cell tumors. BCOR-ITD rearranged tumors commonly manifest as spindle cell sarcomas and many of them display low cellularity with monomorphous cell morphology and myxoid background resembling benign fibroblastic tumors. We present an intriguing case report of a 5-year-old boy diagnosed with a moderately cellular mandibular spindle cell tumor exhibiting BCOR-ITD rearrangement which was initially misdiagnosed as an odontogenic fibromyxoma. This case report illustrates the histological and immunophenotypic findings of BCOR-ITD rearranged sarcoma, requiring a comprehensive immunohistochemical panel and additional molecular tests for accurate diagnosis.