Rosette-forming epithelioid osteosarcoma in childhood: a case report

Osteosarcoma with epithelioid appearance and a rosette-like configuration is a rare, recently reported variation in osteogenic sarcoma, which is thought to be associated with a poor prognosis. We report an unusual pediatric case of rosette-forming epithelioid osteosarcoma with poor response to neoadjuvant chemotherapy and repeated local recurrence following surgical resection. A 6-year-old boy presented with a progressive swelling and pain around the right knee for 25 days before admission. Plain X-ray and MRI showed an ill-defined, expansile, and osteolytic lesion involving the cortical and medullary region of right distal femur with varying degrees of mineralization, and periosteal reaction, extending to surrounding soft tissue. Punch biopsy and subsequent surgical specimens showed a tumor composed of epithelioid cells predominantly arranged in a rosette-like structure, or between dilated blood vessels showing a hemangiopericytoma-like appearance, occasionally with lacelike osteoid deposits. This tumor showed immunoreactivity for epithelial membrane antigen, CD56, CD99, Fli-1, TTF-1, and vimentin. Because of its peculiar morphology, rosette-forming epithelioid osteosarcoma should be differentiated from small cell osteosarcoma, metastatic carcinoma and other tumor with similar morphology, especially neuroblastoma, as well as Ewing's sarcoma, and vitally can be distinguished by the presence of osteoid matrix. Given its poor prognosis, awareness of rosette formation in osteosarcoma is important to avoid misdiagnosis and guide further clinical treatment. This patient experienced twice recurrence during a 15-month period in spite of surgery with wide surgical margins and systemic chemotherapy.