Müllerian adenosarcoma of the uterus. An ultrastructural study of four cases

Four cases of uterine müllerian adenosarcoma, a distinctive form of mixed müllerian tumor, were studied by light and electron microscopy. All tumors showed the characteristic histologic pattern of benign neoplastic glands within sarcomatous stroma. Ultrastructurally, both mesenchymal and epithelial cells were seen. The mesenchymal cells showed some features of endometrial stromal cells, including the presence of intracytoplasmic collagen fibers. The epithelial cells formed glands, which resembled benign endometrial glands and were separated from the stroma by a well‐defined basal lamina. No transitional cells between the epithelial and mesenchymal cells were seen. The ultrastructural features of these tumors suggest that the sarcomatous portion is of endometrial stromal origin. The glandular portion may arise, along with the stroma, from multipotential stem cells, or the glands may be non‐neoplastic entrapped endometrial glands stimulated by the stroma and thus appearing to form an integral part of the tumor.