Borderline and malignant Brenner tumors make up about 5% of all Brenner tumors. The majority of patients are over 50 years of age. The presentation is usually abdominal mass or pelvic pain. About 10% of malignant Brenner tumors are bilateral. Most cases are organ-confined at the time of diagnosis. Grossly, malignant Brenner tumors are large and may be cystic with mural nodules or entirely solid. Malignant Brenner tumors are composed of cytologically malignant transitional cells with stromal invasion. A component of typical (benign) Brenner tumor (see top of the image) or borderline Brenner tumor is present within the tumor.