Epithelioid osteosarcoma of the scapula.

Epithelioid and epithelial neoplasms of bone are rare. They include different epithelioid variants of vascular lesions, osteoblastoma, chondroblastoma and most importantly metastatic carcinoma. Up to now, only few cases of epithelioid osteosarcoma were described. In this case the authors report a 53-year-old patient presented with a medical history of chronic shoulder pain for 3 years. Magnetic resonance imaging (MRI and computed tomography (CT) showed a destructive, partially calcified osseous lesion of the scapula with expansion into the surrounding soft tissue, suggestive of a primary bone tumor. Histologically, the tumor consisted of epithelioid cells with expression of cytokeratine and the lesion was primarily diagnosed as metastatic carcinoma. With regard to the MRI morphology untypical for metastatic disease the histopathologic slides were re-evaluated and detection of tumor osteoid led to the diagnosis of epithelioid osteosarcoma. Chemotherapy was initiated, however follow-up imaging studies showed rapidly progressive disease of both primary tumor and lung metastases. In conclusion, epithelioid neoplasms of the bone are extremetumourly rare and must be distinguished from metastatic carcinoma. Despite the presence of cytokeratine positive cells a thorough histological evaluation is mandatory and osteoid detection is essential in order to establish the correct diagnosis and further treatment. Key words: osteosarcoma, epithelioid, aneurysmal bone cyst, chondrosarcoma, pathology, immunohistochemistry.