Immunohistochemical study of uterine stromal sarcoma and rhabdomyosarcoma

The cytoplasmic filament composition of two pure high-grade endometrial stromal sarcomas and five pure endometrial rhabdomyosarcomas was studied using the immunoperoxidase avidin-biotin method. Ultrastructural correlates were performed on the same tissues. While four of the seven tumors presented as high-grade undifferentiated neoplasms, they were readily categorized on the basis of immunocytochemical findings in which the five rhabdomyosarcomas were positive for muscle-specific actin (HHF 35) and the two stromal sarcomas were positive for vimentin only. Ultrastructure on the HHF 35-positive cases showed the presence of thick filaments and Z-band material, whereas the other tumors showed no cytoplasmic differentiation. Muscle-type actin differs stromal cells, and is useful when used in conjunction with a panel of antibodies in the categorization of undifferentiated endometrial sarcomas.