Undifferentiated High-Grade Pleomorphic Sarcoma of the Posterior Mandible: A Report of a Rare Case.

Undifferentiated pleomorphic sarcoma (UPS) is a high-grade mesenchymal malignancy that can closely resemble benign giant-cell-rich lesions such as central giant cell granuloma (CGCG), especially on limited biopsies. We report a case of a female patient with an enlarging mandibular swelling and an expansile osteolytic lesion that was initially diagnosed as CGCG based on an incisional biopsy showing multinucleated giant cells in a fibroblastic stroma. However, extended immunohistochemistry and the aggressive radiologic features supported a revised diagnosis of giant-cell-rich variant UPS. This case highlights the potential for diagnostic confusion on insufficient samples and emphasizes the importance of adequate tissue sampling, correlation with imaging, and comprehensive ancillary testing when evaluating destructive mandibular lesions.