ObjectiveTo explore the clinicopathologic features, diagnosis and differential diagnosis of epithelioid sarcoma(ES).MethodsThe clinical data, histopathologic observation and immunohistochemical staining were studied in 13 cases of ES.Correlation of INI-l and CyclinD1 protein expression was analyzed.ResultsAmong the 13 cases of ES, 4 were conventional ES and 9 were of proximal-type ES.Proximal-type ES consisted of epithelioid cells, which showed an infiltrative growth pattern with nodular and sheet arrangement.Conventional ES consisted of epithelioid cells and spindle cells, with a granuloma-like pattern.The immunohistochemical study showed expression of Vimentin, CKpan, CD34, EMA, CyclinD1.The immunostain for Desmin, S100, which was focal and weak was found.CD31, CA125, HMB45 and MelanA were negative in all cases.The loss of INI-1 was found in 77.8%（7/9）and 75.0%（3/4） in the conventional ES and the proximal-type ES，respectively.There were no significant differences in negative rate of INI-1 protein between the conventional ES and the proximal-type ES（P＞0.05）.The loss expression of INI-1 protein is not associated with the high expression of CyclinD1 protein（P＞0.05）.ConclusionsOwing to low incidence, pitfalls in diagnosis of ES sometimes are encountered.Immunostaining for INI-1 combined with other commonly used markers (Vimentin, CKpan, EMA and CD34) will be helpful for correct diagnosis.Upregulation of CyclinD1 expression and loss of INI-1 expression was found in ES and there is not association between the two.