Role of electron microscopy in metastatic endometrial stromal tumors.

Endometrial stromal tumors may pose a problem in diagnosis when they appear as metastatic lesions without a known primary tumor. To determine the usefulness of electron microscopy in identifying them in these situations, optimally fixed low-grade stromal sarcomas (five), normal endometrial specimens (six), and malignant mesodermal mixed tumors (four) were studied. The endometrial stromal sarcomas had a general resemblance to normal proliferative endometrial stroma, being composed of undifferentiated cells, fibroblasts, and myofibroblasts. One stromal tumor showed evidence of partial epithelial differentiation. One of the four malignant mesodermal mixed tumors had a fibrosarcomalike component, but there was insufficient resemblance to normal endometrial stroma to indicate a relationship between the two. Together with a review of the literature, this study indicates that electron microscopy is useful in the diagnosis of low-grade endometrial stromal tumors by demonstrating characteristic cellular findings as well as a lack of features specific for other round cell and spindle cell neoplasms.