Cytohistologic Diagnosis of Rosette‐Forming Epithelioid Osteosarcoma

Rosette-forming epithelioid osteosarcoma is an extremely rare type of osteosarcoma. This report describes a man in his early 50s with a destructive right iliac bone/acetabulum mass showing osseous destruction and extensive soft tissue involvement. Cytohistologic examination revealed osteosarcoma with epithelioid neoplastic cells arranged in rosettes. The neoplastic cells were immunoreactive for SATB2, TTF1, and CDX2. The osteoid was better appreciated in the H&E-stained materials. The cytohistological features, immunohistochemical profile, and differential diagnoses are discussed. Attention to details regarding the identification of osteoid in both cytology and histology materials is emphasized.