Brenner tumors are uncommon tumors that are part of the surface epithelial-stromal tumor group of ovarian neoplasms. The majority of these tumors are benign and incidental findings on pelvic examination or at laparotomy.
On gross pathological examination, they are solid, sharply circumscribed and pale yellow-tan in colour. 90% are unilateral (arising in one ovary, the other is unaffected). The tumors can vary in size from less than 1 cm to 30 cm. Borderline and malignant Brenner tumors are possible but each are rare. Histologically, there are nests of transitional-type epithelial cells with longitudinal nuclear grooves (coffee bean nuclei) lying in abundant fibrous stroma.
Transitional cell carcinoma is an even more rare entity, in which neoplastic transitional epithelial cells similar to transitional cell carcinoma of the bladder are seen in the ovary, without the characteristic stromal/epithelial pattern of a Brenner tumor.
Brenner tumors very rarely can occur in other locations, including testis.