Extrauterine mixed mesodermal tumors. An immunohistochemical study

Mixed mesodermal tumors are uncommon outside the uterus. Nine extrauterine mixed mesodermal tumors (eight ovarian and one extra-genital) were selected for histochemical and immunoperoxidase study. In eight cases, both epithelial and mesenchymal elements were malignant (chondroid in six, rhabdomyoid in four, and osteoid in two). One ovarian tumor was an adenosarcoma. All cases were stained with periodic acid-Schiff with and without diastase and for α₁-antitrypsin, myoglobin, keratin, vimentin, muscle-specific actin, and α₁-antichymotrypsin, by using the avidin-biotin-immunoperoxidase method. The periodic acid - Schiff-positive, diastase-resistant droplets in several of the tumors showed peripheral α₁-antitrypsin positivity. Keratin delineated epithelial areas well in seven cases, and rhabdomyoid differentiation was confirmed with myoglobin in four cases. However, squamous elements in one tumor were falsely positive for myoglobin. We concluded that despite occasional cross-reactivity, carefully interpreted immunoperoxidase stains can be useful in distinguishing epithelial and mesenchymal elements in these tumors.