Giant primary hepatic osteosarcoma: A rare case report and review of the literature.

OBJECTIVE: Primary hepatic extraskeletal osteosarcoma (PHOS) is an extremely rare and aggressive malignant tumor originating in the liver with no primary skeletal lesion. Less than 1% of all extraskeletal osteosarcomas occur in the liver, often presenting as a large abdominal mass with poor prognosis. CASE PRESENTATION: F-FDG) uptake. Histopathological analysis confirmed the diagnosis, showing atypical mesenchymal cells producing osteoid matrix with strong special AT-rich sequence-binding protein 2 (SATB2) positivity and negative epithelial markers. DISCUSSION: Imaging characteristics and immunohistochemical profiling were crucial in differentiating PHOS from hepatocellular carcinoma and metastatic osteosarcoma. The case supports the metaplasia theory of PHOS pathogenesis and highlights its radiologic-pathologic correlation, especially the "cloud-like" enhancement on imaging corresponding to unmineralized osteoid and vascular proliferation. CONCLUSION: This case highlights the diagnostic challenge and clinical significance of PHOS. Comprehensive imaging and pathological evaluation are essential for accurate diagnosis. Due to its rarity and aggressiveness, PHOS requires individualized management strategies, typically involving surgery and adjuvant therapies despite limited evidence-based guidelines.