OBJECTIVETo study the neoplasm with perivascular epithelioid cell differentiation (PEComa) with respect to their morphologic, immunohistochemical and clinical phenotypes.

METHODSThree PEComas were included in this study, one located at the left uterine horn, and two presented as a mass in the uterine corpus. The tumors were examined by histopathology and immunohistochemistry.

RESULTSThe lesions were composed of spindle, blunt epithelioid cells, with foci of, or scattered, cells showing adipose differentiation in two cases. The myomelanocytic differentiation was demonstrated, proving the diagnosis as PEComa. Mild nuclear atypia and focal necrosis was observed in one lesion, and the rest two showed malignant morphologic phenotypes including moderate nuclear atypia and coagulative necrosis. The mitotic and Ki67-labelling indices ranged from 0.5/10 HPF to 14/10 HPF and 0.6% to 7.0%, respectively. All of the three patients remain alive. Malignant nature of the two lesions with worrisome morphology was confirmed by occurrence of metastases after hysterectomy.

CONCLUSIONPEComa is a rare tumor, occurring preferentially in the uterus. It is regarded as a tumor with uncertain malignant potential, but a minority of them shows malignant clinical behaviors. Some pathologic parameters including large tumor size, sheet-like necrosis, marked nuclear atypia, elevated mitotic index (> or = 10/10 HPF), aberrant mitotic figure and vascular invasion may help to establish a diagnosis of malignant PEComa.