Two unusual and rare forms of Brenner tumors are reported. T h e first group included seven patients with an unusual proliferation of Brenner epithelium to the degree that their tumors resembled low-grade papillary neoplasms of the bladder, but they nonetheless lacked cytologic characteristics of overt carcinoma. All tumors were clinically Stage I at initial diagnosis, and none extended or metastasized beyond the ovary. T h e second group included seven cases designated as malignant Brenner tumors because they contained histologically malignant epithelium as well as areas of the typical Brenner tumor. Each neoplasm had transitions between the two areas. Six of the seven neoplasms were confined to the ovary at the time of initial diagnosis. Of the seven women, three developed recurrence and metastasis following surgery. The mean age of women with proliferative Brenner tumors was younger than women with malignant ones. A specific designation of malignant and proliferative categories is justified and recommended, since the proliferative tumor is benign and should not be confused with its frankly malignant counterpart. Although from this study there is no proof of origin of Brenner tumors, the concept of origin from pluripotential surface epithelium of the ovary is s u p ported, in view of the urinary tract-like (urothelial) epithelial tumors found. These tumors reflect the capacity of the ovary to produce neoplasms that resemble those arising in other organs in the abdominal cavity, i.e., uterus, peritoneum, adrenal, and kidney, as well as bladder. No conclusions could be drawn regarding a functional effect of these neoplasms. HE TYPICAL BRENNER TUMOR IS A DISTINC-* Present address:
