Benign Brenner Tumour: Understanding Your Pathology Report

Section Editor: Kianoosh Keyhanian MD FRCPC
August 29, 2026

A benign Brenner tumor is a noncancerous (benign) growth that starts in the ovary. Under the microscope, it is made of small nests of cells that resemble the lining of the urinary tract, called urothelial cells. These nests sit inside dense, firm supporting tissue called stroma. The tumor is named after Fritz Brenner, the pathologist who described it in 1907.

Brenner tumors are uncommon. They make up roughly 1 to 5 percent of ovarian epithelial tumors and about 2 percent of all ovarian tumors. Most are found in adults over the age of 40, and they are most common around and after menopause. The great majority are benign. Most are small, and many are found incidentally when an ovary is removed for another reason.

A benign Brenner tumor is not cancer, and it does not spread to other parts of the body. This article will help you understand what this diagnosis means on your pathology report, what each term means, and why it matters for your care.

What causes a benign Brenner tumor?

The cause of a benign Brenner tumor is not fully understood. It is not an inherited condition, and having one does not mean your relatives are at risk.

The leading explanation involves small clusters of cells called Walthard nests. These are collections of urothelial-type cells that are commonly found on and near the fallopian tube, and they are considered a normal finding. A benign Brenner tumor is thought to grow from one of these clusters, or from a similar change in the surface lining of the ovary called transitional metaplasia. Pathologists often find Walthard nests in the same specimen as a Brenner tumor, which supports this explanation.

Genetic changes are uncommon in these tumors. Some cases have had extra copies of a gene called MYC. MYC normally helps control how often a cell divides, and extra copies can push cells to divide more than they should. This is a research finding. It is not tested for in routine practice, and it will not appear on your pathology report.

What are the symptoms?

Most people with a benign Brenner tumor have no symptoms. These tumors are usually small, and most are found by chance, either on an imaging test or when an ovary is removed during surgery performed for another reason. When symptoms do occur, they usually fall into two groups.

Symptoms from the size of the tumor — A large tumor can make the abdomen feel swollen or full. It may also cause discomfort or pain in the lower abdomen or pelvis.
Symptoms from hormone activity — In some Brenner tumors, the supporting tissue around the cell nests starts producing estrogen. Extra estrogen can cause vaginal bleeding after menopause, or a change in menstrual bleeding before menopause. It can also thicken the lining of the uterus, which your doctor may investigate separately.

These symptoms have many possible causes, and none of them is specific to a Brenner tumor. A doctor should assess any bleeding after menopause.

How is the diagnosis made?

A benign Brenner tumor is diagnosed after the tumor is removed surgically and examined under the microscope by a pathologist. In many cases, the tumor was not the reason for the operation. It is often an unexpected finding in an ovary removed for a cyst, another tumor, or as part of a hysterectomy.

Imaging tests such as ultrasound, CT, or MRI may show a firm, solid mass in the ovary, often containing calcium deposits. Because the tumor is mostly fibrous tissue, it can look very similar to other solid ovarian tumors such as an ovarian fibroma or a thecoma. Imaging cannot tell these apart with certainty, so the diagnosis is made from the tissue itself.

During the operation, the surgeon may request an intraoperative consultation, also called a frozen section. The pathologist examines a piece of the tumor while the patient is still in the operating room and gives a preliminary diagnosis within minutes. The pathologist makes the final diagnosis later, once the whole tumor has been examined in detail.

The pathologist samples the tumor carefully, including any cystic or papillary areas. This matters because a borderline or malignant Brenner tumor almost always contains a benign Brenner component beside it. Thorough sampling helps the pathologist confirm that the entire tumor is benign. When the appearance under the microscope leaves any question about the diagnosis, additional stains may be performed, as described in the next section.

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

A benign Brenner tumor is an ovarian tumor built from nests of urothelial-type cells set in dense fibrous tissue. To the naked eye, it is usually a firm, solid, pale mass, often gritty when cut because of calcium deposits. Under the microscope, the pathologist looks for the following features.

Nests of urothelial-type cells — Small, well-defined groups of uniform cells that resemble the lining of the bladder. Your report may call these transitional-type cells, which is another name for the same cells.
Bland, uniform nuclei — The nucleus is the part of the cell that holds the genetic material. In this tumor, the nuclei are oval and uniform in size, with fine chromatin and small nucleoli. Many have a lengthwise fold called a groove, which gives them a coffee-bean appearance.
Dense fibrous stroma — The nests sit in thick supporting tissue. This tissue is often hardened, which pathologists describe as hyalinized.
Small cystic spaces — Some nests contain tiny cyst-like spaces filled with pink material, mucus, or fluid. These spaces may be lined by urothelial, mucus-producing, ciliated, or cube-shaped cells.
Calcifications — Deposits of calcium are common within the fibrous tissue. Calcification is a normal finding in this tumor and is not a sign of cancer.
Very few dividing cells — A dividing cell caught in the act is called a mitotic figure. In a benign Brenner tumor, these are rare, which reflects how slowly the tumor grows.
No invasion — The cell nests stay within their boundaries and do not grow destructively into the surrounding tissue. The absence of invasion is one finding that confirms the tumor is benign.

Immunohistochemistry

Immunohistochemistry is a laboratory test that uses antibodies to detect specific proteins inside cells. Pathologists use it when the appearance of a tumor under the microscope could fit more than one diagnosis. For a benign Brenner tumor, the protein pattern helps confirm the urothelial-type nature of the cell nests and separates this tumor from other ovarian tumors that can look similar. If these tests were performed, your report lists the protein names with positive or negative beside each one.

GATA3. Positive. GATA3 is typical of urothelial-type cells and is one of the most useful markers for this tumor.
CK7. Positive. Cytokeratin 7 is a structural protein found in many lining cells, including urothelial cells.
p63. Positive. p63 is found in urothelial and squamous-type cells.
Androgen receptor. Positive. The androgen receptor is a protein that responds to male-type hormones. It is commonly present in Brenner tumors and does not mean the tumor is hormone-driven.
Uroplakin, thrombomodulin, and S100P. Positive. These proteins are also characteristic of urothelial cells and support the diagnosis.
PAX8. Negative. PAX8 is present in most other ovarian epithelial tumors. A negative result is expected in a Brenner tumor and helps separate it from those other tumors.
CK20. Negative. Cytokeratin 20 is found in cells of the digestive tract. A negative result argues against a tumor that spread from the bowel.
Estrogen receptor and progesterone receptor. Negative in the cell nests. The estrogen and progesterone receptors are often positive in the surrounding supporting tissue, which is normal.

Not every case requires these tests. Many benign Brenner tumors have such a characteristic appearance that the pathologist can diagnose them without additional stains.

How is a benign Brenner tumor different from a borderline or malignant Brenner tumor? Ovarian

Brenner tumors are divided into three groups: benign, borderline, and malignant. The great majority are benign. What separates the three is how the cell nests grow, and whether they invade the surrounding tissue.

Benign Brenner tumor — Orderly nests of bland cells in fibrous tissue, with no complex finger-like growths and no invasion.
Borderline Brenner tumor — The cells form finger-like projections and look more abnormal than in a benign tumor, but they still do not invade. A borderline Brenner tumor is not cancer, and the outlook after surgery is excellent.
Malignant Brenner tumor — The tumor cells invade the surrounding tissue. A malignant Brenner tumor is a cancer, and it accounts for fewer than 5 percent of all Brenner tumors.

Borderline and malignant Brenner tumors almost always contain a benign Brenner tumor alongside them. Pathologists take this to mean these tumors can develop from a benign one over time. That progression is very rare, and it does not happen to most benign Brenner tumors. That is why your pathologist examined the whole tumor rather than a single piece. If your report says the tumor is benign, the pathologist looked for these changes and did not find them.

What other findings may be described in the report?

Along with the diagnosis of a benign Brenner tumor, your pathology report may describe several other features of the tumor and the surrounding tissue.

Tumor size — The report gives the greatest dimension in centimeters. Most benign Brenner tumors are under 2 cm, though larger ones occur. Size does not change the fact that the tumor is benign.
One or both ovaries — Almost all benign Brenner tumors involve one ovary only. Involvement of both ovaries is uncommon and does not, on its own, change the diagnosis.
Another tumor in the same ovary — A second ovarian tumor is found alongside a Brenner tumor in up to 30 percent of cases. The most common partner is a mucinous cystadenoma, and a mature cystic teratoma is also seen. Both are noncancerous, and your report will name each tumor separately.
Walthard nests — The report may mention these small clusters of urothelial-type cells near the fallopian tube. They are a normal finding and are commonly seen with Brenner tumors.

What happens after this diagnosis?

A benign Brenner tumor is a noncancerous ovarian tumor. It does not spread to other parts of the body, and it is considered cured once it has been completely removed. Because it is not cancer, it is not given a grade, and it is not assigned a stage. Grading and staging describe how a cancer is behaving and how far it has spread, and neither applies here.

What you and your gynecologic team discuss next depends on how the tumor was found, your age, and your overall situation. Points the team may raise include:

No further cancer treatment — Chemotherapy and radiation therapy are not used for this tumor, because it is benign.
Recurrence is not expected — Once removed, a benign Brenner tumor does not come back.
Hormone-related symptoms — If the tumor was producing estrogen and caused abnormal bleeding, that usually settles after the tumor is removed. If the lining of the uterus was thickened, your doctor may want to look at it separately.
Other findings in the specimen — If another tumor was found in the same ovary, the follow-up is guided by that diagnosis rather than by the Brenner tumor.
Incidental discovery — When a Brenner tumor is found unexpectedly in an ovary removed for another reason, it usually adds nothing to the treatment plan already in place.

Most people need no further treatment. Your doctor will tell you whether any follow-up is recommended in your situation.

Questions to ask your doctor

Was the diagnosis confirmed as a benign Brenner tumor, with no borderline or malignant areas?
How large was the tumor?
Was the tumor in one ovary only, or were both ovaries involved?
Was another type of tumor found in the same ovary or the other ovary?
Was the tumor the reason for my surgery, or was it found unexpectedly?
Was the ovary removed, or only the tumor?
Were any special stains performed to confirm the diagnosis, and what did they show?
Did the tumor show any hormone activity, and could that explain my symptoms?
Should the lining of my uterus be checked?
Do I need any further treatment?
Is any follow-up imaging or appointment recommended?
What symptoms should prompt me to contact you?