Ultrastructure of malignant Brenner tumor of the ovary

Six malignant Brenner tumors of the ovary were studied electronmicroscopically. The histologic features of the tumors resemble to those of nonkeratinized squamous cell carcinoma of the uterine cervix. The ultrastructural features of malignant Brenner tumor included intracytoplasmic glands and cysts, presence of cilia, abundant glycogen, numerous desmosome-tonofilament complex, of which the cilium is most characteristic in the ovarian surface epithelium or Mullerian epithelium, but not in uroepithelium. Desmosome-tonofilament complex, the ultrastructure specific for the squamous epithelium, was not seen in the uroepithelium. We conclude that the appearance of cilium in malignant Brenner tumor indicates that the tumor is derived from the Mullerian epithelium, and that the presence of desmosome-tonofilament complex evidences that the tumor cells have differentiated into squamous epithelium. Our findings have proved that the malignant Brenner tumor arises from the Mullerian epithelium and recapitulates the vaginocervical epithelium.