Rosette formation in osteosarcoma.

Rosette formation is a rare, recently reported variation in osteogenic sarcoma and is thought to be associated with a poor prognosis. We report two cases of rosette forming osteosarcoma, one with poor response and other with total necrosis following chemotherapy. Pathologists should be aware of rosette formation in osteosarcoma to avoid misdiagnosis as other rosette forming tumors of bone especially PNET/Ewings sarcoma. In our opinion rosettes in an osteosarcoma should be documented both from a differential diagnostic point of view and also to elucidate definitive prognostic implications.