[Clinico-pathologic study of Ewing's sarcomas of bone and soft tissue and peripheral primitive neuroectodermal tumors].

Objective: To study the diagnosis and differentiation of EW and PNET.
Methods: Fourteen cases of Ewing's sarcomas (EW) and peripheral primitive neuroectodermal tumors (PNET) were studied by light microscopy, immunohistochemistry and electron microscopy (EM). Twelve cases were followed up. Schmidt criterion was used for the differential diagnosis of EW and PNET.
Results: There were 6 cases of EW and 8 cases of PNET. Six of 8 PNET cases had Homer-Wright (H-W) rosettes. In this series, 12/14 cases were positive for O13 (HBA71) staining. NSE was positive in 3 cases of EW. All PNET cases were positive for neural markers, and 5 of them were positive for more than two of these markers. Electronmicroscopically, there were neurosecretory granules (4/4 cases), nerve-like protrusions and microfilaments (1/4 case) in PNET. In 3 of 6 EW and 1 of 6 PNET, PAS staining was positive. During the follow-up period from 2 months to 5 years, 3 cases with intraosseous EW remain alive and free of tumor. The remaining patients are dead or having their tumors metastasized.
Conclusion: EW is more primitive in cell differentiation, while PNET has more neural differentiation. The presence of H-W rosettes is an important morphologic feature of PNET. To differentiate EW from PNET is of clinical significance O13 is a useful marker for the diagnosis of EW/PNET.