Benign Brenner tumour

by Emily Goebel, MD FRCPC
August 27, 2025

A benign Brenner tumor is a noncancerous growth that starts in the ovary. It is composed of nests of cells resembling the lining of the urinary tract, known as urothelial epithelium, surrounded by dense supportive tissue called stroma. Because this tumor is benign, it does not spread to other parts of the body and does not turn into cancer.

How common is a benign Brenner tumor?

Brenner tumors are uncommon but not rare. They account for about 5 percent of all benign ovarian epithelial tumors. They are most often found in adults between the ages of 40 and 70, although they can occasionally be seen in younger women under 30 or in older women over 80.

Where are benign Brenner tumors found?

Most Brenner tumors are found in one ovary only, but in rare cases they can develop in both ovaries. Very rarely, Brenner tumors have also been reported outside the ovary.

What are the symptoms of a benign Brenner tumor?

Most patients with a benign Brenner tumor have no symptoms. In many cases, the tumor is discovered by chance when the ovary is removed for another reason.

If the tumor is large, it may cause the abdomen to become swollen or painful. In some cases, Brenner tumors produce hormones. When this happens, they can cause symptoms such as abnormal vaginal bleeding or other changes related to hormone activity.

What causes a benign Brenner tumor?

The exact cause of Brenner tumors is not fully understood. Some may develop from small nests of transitional-type cells called Walthard rests, which can be found near the fallopian tubes. Rare cases associated with another ovarian tumor called a teratoma may have their origin in germ cells, which are the cells that normally develop into eggs.

Genetic changes have been studied in Brenner tumors, but mutations are uncommon. In some tumors, an increase in copies of a gene called MYC has been reported.

How is this diagnosis made?

The diagnosis of a benign Brenner tumor is usually made after the tumor is surgically removed and examined by a pathologist. The pathologist looks at thin sections of the tumor under the microscope to see the typical features, which include nests of urothelial-type cells surrounded by fibrous tissue.

Special laboratory tests, such as immunohistochemistry, may also be performed. These tests look for specific proteins in the tumor cells that help confirm the diagnosis and rule out other types of ovarian tumors.

What does a benign Brenner tumor look like under the microscope?

Under the microscope, Brenner tumors are composed of small nests of uniform cells that look like urothelial cells. These nests sit within dense fibrous stroma. Some nests contain tiny cyst-like spaces filled with pink material, mucus, or fluid. The cysts may be lined by urothelial, mucinous, ciliated, or cuboidal cells.

The tumor cells are bland, meaning they do not look abnormal. They are uniform in appearance with oval-shaped nuclei, occasional small folds called grooves, and fine chromatin. Small nucleoli may also be seen. Pathologists may also see calcifications, areas of dense hyalinized stroma, or mucinous changes. Mitotic activity, which refers to dividing cells, is very low.

When Brenner tumors are associated with mucinous tumors, the mucinous component is almost always a benign mucinous cystadenoma.

What other tests may be ordered to confirm the diagnosis?

Pathologists sometimes perform a test called immunohistochemistry, which uses special stains to highlight proteins inside tumor cells. These stains help confirm the diagnosis and rule out other types of ovarian tumors.

Brenner tumors usually test positive for proteins such as GATA3, CK7, p63, S100P, androgen receptor, uroplakin, and thrombomodulin. They are usually negative for proteins such as CK20, PAX8, estrogen receptor, and progesterone receptor. These results help confirm the diagnosis because they are consistent with the expected profile of a Brenner tumor.

Is staging used for benign Brenner tumor?

No. Because Brenner tumors are benign, they are not staged in the same way that cancers are staged. Staging is not necessary because these tumors do not spread or behave like cancer.

What is the prognosis for a benign Brenner tumor?

The prognosis for patients with a benign Brenner tumor is excellent. These tumors are noncancerous and do not have any risk of recurrence or progression after removal. Once the tumor is removed, no further treatment is usually needed.

Questions to ask your doctor

• Was the tumor confined to one ovary or both?

• Was the tumor associated with another type of ovarian tumor?

• Did the tumor show any hormone-producing activity?

• Is any follow-up recommended after surgery?