Osteosarcoma with epithelioid features. An immunohistochemical study.

We report a case of osteosarcoma with coexpression of epithelial and mesenchymal markers immunohistochemically of the second lumbar vertebra in a 49-year-old man. Histologically, the tumor largely showed typical patterns of osteosarcoma with lacelike osteoid deposition and chondroblastic and fibroblastic areas. Immunoreactivity for osteocalcin (human bone gamma-carboxyglutamic acid-containing protein) was demonstrated in most of these tumor cells. Both primary and recurrent tumors contained areas that were composed of epithelioid cells with an alveolar pattern and a trabecular arrangement that resembled carcinoma. Some of the epithelioid cells gave positive reactions for cytokeratin and epithelial membrane antigen. On extensive examination, no other site of malignancy was detected. There have been a few reports of osteosarcomas with epithelioid cells, but to our knowledge, the immunohistochemical properties of this type of tumor have not been reported previously. This is an unusual case of osteosarcoma with epithelioid features.