Ovarian Brenner tumors. I. Metaplastic, proliferating, and of low malignant potential.

In several studies, attempts were made to establish criteria for distinguishing malignant Brenner tumors from proliferating and low malignant potential ones. Although these criteria can be applied to the majority of cases, there still exist tumors that present problems in classification. In applying the World Health Organization (WHO) criteria for Brenner tumors, the most important feature for distinguishing the intermediate forms from the malignant ones is the presence of stromal invasion in the latter. This feature has generally been considered difficult to employ because of the fundamental fibroepithelial nature of Brenner tumors, the stroma being derived from the ovarian stroma. A logical and relatively easily applicable classification of Brenner tumors is presented in this report. Although more complex than the WHO classification, it includes newly recognized variants of the Brenner tumor and avoids using the same terminology to describe different types and degrees of epithelial abnormalities. Fourteen unusual Brenner tumors were studied, intermediate between typical benign and frankly malignant ones, and were classified into 3 categories representing progressive epithelial abnormalities. These include metaplastic, proliferating, and tumors of low malignant potential. In none of these does stromal invasion occur. Each of these categories corresponds to a particular urothelial abnormality or neoplasm. Through this classification, a better understanding of the morphology and biologic behavior of unusual types of Brenner tumors can be expected.