Abstract
A case of mullerian adenosarcoma arising in the endometrium was studied by light and electron microscopy before and after radiation treatment. The tumor was composed of malignant stroma containing undifferentiated mesenchymal cells admixed with mature fibroblasts and other cells that contained crystalloids. The surface epithelium was lined by epithelial cells with and without cilia, similar to the normal surface epithelium cells of the uterus. High-dose therapeutic irradiation eliminated the undifferentiated mesenchymal cells from the tumor but did not alter the morphology of other epithelial and mesenchymal elements. The immaturity of mesenchymal cells and their radiosensitivity coupled with the ultrasonographic evidence of growth of the tumor point to the probable malignant nature of this neoplasm.