FLI-1 distinguishes Ewing sarcoma from small cell osteosarcoma and mesenchymal chondrosarcoma.

Small cell osteosarcoma and mesenchymal chondrosarcoma are 2 primary bone tumors with a small round blue cell component, which can mimic the appearance of Ewing sarcoma. Distinguishing these tumors from each other on biopsy material is important clinically, as optimal therapy differs according to the tumor type. However, separating these entities on morphology alone can be challenging. FLI-1 has been described to be a useful marker for Ewing sarcoma, particularly when hematolymphoid markers are negative. In small cell osteosarcoma and mesenchymal chondrosarcoma, the FLI-1 staining pattern has not been adequately characterized. Using a monoclonal FLI-1 antibody, nuclear immunoreactivity in tumor cells was evaluated in 10 small cell osteosarcomas, 10 mesenchymal chondrosarcomas, and 8 Ewing sarcomas, together with a number of other small, round, blue cell tumors. None of the small cell osteosarcomas or mesenchymal chondrosarcomas exhibited FLI-1 staining in the tumor cells, in contrast to the positive nuclear FLI-1 staining in the stromal endothelial cells. In comparison, 6 of the 8 Ewing sarcomas showed moderate-to-strong nuclear FLI-1 staining of the tumor cells in addition to strong staining of the stromal endothelial cell nuclei. With the exception of lymphoblastic lymphomas, FLI-1 positivity was not seen in the other small round blue cell tumors examined. These findings show that, in contrast to Ewing sarcoma, small cell osteosarcoma and mesenchymal chondrosarcoma lack FLI-1 immunoreactivity. FLI-1 is therefore useful in the differential diagnosis of small round blue cell tumors of the bone.

Small round blue cell tumors in bone: prognostic factors correlated to Ewing's sarcoma and neuroectodermal tumors.

Ewing's sarcoma and peripheral neuroectodermal tumors are the most common small round blue cell tumors of bone. Accurate prognostic factors are required to define guidelines to standardize the treatment modalities and to adapt these modalities to the potential evolution of the disease. The various factors that have emerged in the literature as influences on the outcome of patients with Ewing's sarcoma or peripheral neuroectodermal tumors of bone are considered in this review. The presence of metastases at the clinical onset of the disease represents the most adverse prognostic factor. For nonmetastatic patients, axial location appears to be the most unfavorable factor, despite initial tumor volume, by showing that the tumor burden could be a more appropriate indicator of patient outcome. The importance of a local control of the disease by surgery has been emphasized, and the value of the histopathologic evaluation of the response to chemotherapy has been stressed.