Clear cell carcinoma of the endometrium with lipid-producing activity. Histologic and ultrastructural study...

A case of clear cell carcinoma of the endometrium with lipid-producing activity in a 59-year-old woman was studied by light and electron microscopy. Following a modified radical hysterectomy, the plasma level of cancer antigen 125 (CA125) decreased abruptly. Histologically, the tumor was composed of clusters of large, polygonal cells with either clear or eosinophilic cytoplasm, showing distinct borders and bizarre, pleomorphic nuclei divided into many groups by the connective tissue elements. Abundant lipid droplets in the neoplastic cells were observed by Sudan III stain, and the CA125 antigen was demonstrated in the neoplastic cells. Mitotic figures were difficult to find. Electron microscopically, the tumor cell nuclei were oval or polygonal and sometimes slightly invaginated, with a few prominent nucleoli. The cytoplasm contained abundant lipid droplets, rough endoplasmic reticulum, rod-shaped to round mitochondria, Golgi apparatus, glycogen particles, and free ribosomes. A few small lumina containing microvilli were recognized. These observations suggest that this lesion is a unique type of clear cell carcinoma of the endometrium originating from Müllerian epithelium and possessing lipid-producing activity.