Abstract
Osteosarcoma shows a variety of histologic patterns. Uncommonly, this tumour has an epithelioid appearance, and the rosette formation is more rarely observed.
We report an unusual case of a 12 year-old girl who was referred to us with pain and a mass around her left shoulder with upper limb motor dysfunction. X-ray showed a pathologic fracture of the proximal humerus. Biopsy was performed. Histologically, the neoplasm is characterized by a small multinodular growth pattern. The tumoral cells have plasmocitoid or epithelioid shape and they are arranged forming rosettes. Sheet-like osteoid deposition was found. Inmunohistochemical studies revealed the tumour to be positive for epithelial membrane antigen (EMA), vimentine, CD-99 and neuron-specific enolasa (NSE).
The rosette-forming osteosarcoma has an aggressive clinical behaviour. The location, clinical features and chemotherapy effect are important prognostic factors. Histological differential diagnosis includes small cell osteosarcoma, metastatic neuroblastoma, PNET and metastatic carcinoma.
Correspondence should be addressed to Professor Stefan Bielack, Olgahospital, Klinikum Stuttgart, Bismarkstrasse 8, D-70176 Stuttgart, Germany. Email: s.bielack@klinikum_stuttgart.de
