Cellular Fibroma of the Ovary: Understanding Your Pathology Report

Section Editor: Kianoosh Keyhanian MD FRCPC
August 29, 2026

A cellular fibroma is a noncancerous (benign) tumor of the ovary. It grows from fibroblasts, the cells that make the firm supporting tissue found inside the ovary. It belongs to a family of tumors called sex cord-stromal tumors.

The word “cellular” describes what the pathologist sees under the microscope. In an ordinary ovarian fibroma, the tumor cells are spread apart in abundant collagen. In a cellular fibroma, the cells are packed more tightly together, with less collagen between them. That difference in density is the only thing that separates the two diagnoses. Both are benign and treated the same way.

Cellular fibromas occur most often in middle age, at an average of around 50 years. They range in size from under 1 cm to more than 20 cm, and almost all involve one ovary only. A cellular fibroma 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 cellular fibroma of the ovary?

The cause of a cellular fibroma is not known. In most cases, there is no identifiable reason why one person develops this tumor.

A small number of ovarian fibromas of all types occur as part of an inherited condition called nevoid basal cell carcinoma syndrome, also known as Gorlin syndrome. This syndrome is caused by a change in a gene called PTCH1, which normally helps limit how much cells grow. Fibromas linked to the syndrome tend to occur at a younger age, involve both ovaries, form multiple separate nodules, and contain calcium deposits. Most cellular fibromas have nothing to do with Gorlin syndrome, and a single tumor in one ovary in an adult is not a reason to suspect it.

What are the symptoms?

Many cellular fibromas cause no symptoms. Smaller tumors are often found by chance, either during an imaging test performed for another reason or when an ovary is removed for another reason. When symptoms do occur, they usually come from the size of the tumor.

Abdominal or pelvic pain — Discomfort or pressure low in the abdomen or pelvis.
Abdominal swelling — A large tumor can make the abdomen feel full or look enlarged.
Sudden, severe pain — A large ovarian tumor can twist on its blood supply, a problem called torsion. This causes sudden severe pain and needs urgent medical attention.
Fluid in the abdomen — Some fibrous ovarian tumors, particularly large ones, cause fluid to collect in the abdomen. This is called ascites.

A small number of people with a fibrous ovarian tumor develop fluid in both the abdomen and the chest. That combination is called Meigs syndrome. It closely resembles advanced ovarian cancer, and the blood test CA-125 can be raised as well. Many people in this situation are investigated for cancer before the diagnosis is known. The fluid clears on its own once the tumor is removed.

How is the diagnosis made?

A cellular fibroma is diagnosed after the tumor is removed surgically and examined under the microscope by a pathologist. The surgery usually removes the whole ovary, sometimes along with the fallopian tube on the same side. In some cases, the tumor was not the reason for the operation and is found unexpectedly.

Imaging tests such as ultrasound, CT, or MRI show a firm, solid mass in the ovary. Imaging cannot reliably separate a cellular fibroma from other solid ovarian tumors, including cancers. A solid ovarian mass on a scan is usually reported as needing surgery to establish the diagnosis. This is why many people are told a tumor is suspicious before the benign diagnosis is confirmed.

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. That result can change how much tissue the surgeon removes. The pathologist makes the final diagnosis later, once the whole tumor has been examined in detail.

The pathologist samples the tumor in several places and pays close attention to two things: how often the tumor cells are dividing, and whether they look abnormal. These two findings separate a cellular fibroma from its close relatives and from a rare cancer called fibrosarcoma. Because both findings can vary from one part of a tumor to another, thorough sampling matters. When the appearance under the microscope could fit more than one diagnosis, additional stains may be performed, as described below.

What does a cellular fibroma look like under the microscope?

A cellular fibroma is a benign ovarian tumor made of densely packed fibroblasts and the collagen they produce. To the naked eye, it is usually a firm, solid, white or pale tumor. Under the microscope, the pathologist looks for the following features.

Densely packed spindle cells — The tumor is made of long, thin cells called spindle cells, named for their tapered shape. They are usually arranged in bundles, called fascicles, that cross one another. In a cellular fibroma, these cells sit closer together than in an ordinary fibroma.
Less collagen — Supporting tissue remains between the cells, and the report may describe it as hyalinized or fibrotic. There is simply less of it than in an ordinary fibroma.
Bland nuclei — The cells look uniform. Marked variation in the size and shape of the nuclei, which pathologists call nuclear atypia, is not seen in a cellular fibroma. Its absence is one finding that confirms the tumor is benign.
Few dividing cells — A cell caught in the act of dividing is called a mitotic figure. In a cellular fibroma, there are fewer than 4 per 10 high-power fields, the standard microscope area pathologists use for counting.
Degenerative changes — Large or long-standing tumors may show bleeding into the tumor, and areas of tissue death called infarct-type necrosis. This happens when the tumor outgrows its blood supply. Necrosis of this kind is expected in a large fibrous tumor and is not a sign of cancer.

Immunohistochemistry

Immunohistochemistry is a laboratory test that uses antibodies to detect specific proteins inside cells. For a cellular fibroma, these stains confirm that the spindle cells come from the supporting tissue of the ovary. They also separate this tumor from other spindle cell tumors that can look similar. If the tests were performed, the results appear in your report as a list of protein names with the word positive or negative beside each one.

Inhibin and calretinin. Often positive, but usually only in scattered areas. These proteins are made by the ovary’s hormone-producing and supporting cells. Patchy staining supports a fibrous tumor. Strong staining throughout the tumor points instead toward a thecoma, a related tumor.
WT1. Usually positive. WT1 is commonly present in tumors that arise from ovarian supporting tissue.
Estrogen receptor and progesterone receptor. Often positive. The estrogen receptor and progesterone receptor are proteins that respond to female hormones. A positive result is expected and does not mean the tumor is hormone-driven or that hormone treatment is needed.
Other markers. Stains such as desmin, S100, and cytokeratin are usually negative. Negative results help rule out a muscle tumor, a nerve sheath tumor, or a tumor that spread from elsewhere.

Two further tests are used when the tumor is densely cellular, which is often the situation in a cellular fibroma. A reticulin stain outlines the fibers around individual cells, and the pattern differs between a fibrous tumor and an adult granulosa cell tumor. Testing for a change in a gene called FOXL2 can also help. That change is found in most adult granulosa cell tumors and is absent in cellular fibromas, so a negative result supports the benign diagnosis.

How does a cellular fibroma differ from other fibrous tumors of the ovary?

A cellular fibroma sits within a group of related ovarian tumors made of the same spindle cells. What separates them is how tightly the cells are packed, how often they divide, and whether they look abnormal. Your report may use any of the following terms.

Fibroma — Cells spread apart in abundant collagen, with rare dividing cells. Benign.
Cellular fibroma — Cells packed tightly together, with fewer than 4 dividing cells per 10 high power fields and no marked nuclear abnormality. Benign.
Mitotically active cellular fibroma — Cells packed tightly together and dividing more often, at 4 or more per 10 high power fields, but still without marked nuclear abnormality. A mitotically active cellular fibroma behaves benignly in almost all reported cases.
Fibrosarcoma — A rare cancer made of the same kind of cells. Diagnosis requires both frequent cell division and cells that look clearly abnormal throughout the tumor.

The most important distinction is the last one. Frequent cell division alone does not make a tumor a fibrosarcoma. Under current World Health Organization criteria, clear nuclear abnormality must also be present. Tumors that divide often but look bland were once labeled fibrosarcoma, and patients were sometimes treated for a cancer they did not have. If your report says cellular fibroma, the pathologist looked for those abnormal features and did not find them.

What other findings may be described in the report?

Along with the diagnosis of cellular fibroma, your pathology report may describe other features of the tumor and the surrounding tissue.

Mitotic count — The report often gives the number of dividing cells per 10 high-power fields. This number separates a cellular fibroma from a mitotically active cellular fibroma, so it is worth knowing what yours was.
Tumor size — The report gives the greatest dimension in centimeters. Size does not change the fact that the tumor is benign, but it does influence the type of surgery performed.
One or both ovaries — Almost all cellular fibromas involve one ovary only. Involvement of both ovaries is uncommon and prompts a pathologist to consider Gorlin syndrome, particularly in a younger patient.
Adhesions — The report may note whether the tumor was stuck to nearby tissue. This matters more for a cellular fibroma than for an ordinary one, because the rare tumors in this group that recurred were usually adherent or ruptured.
Rupture — The report may state whether the tumor was intact or ruptured before or during surgery.
Other findings in the ovary — The report describes the rest of the ovary and any other tissue removed, including the fallopian tube and, when removed, the uterus.

What happens after this diagnosis?

A cellular fibroma is a benign ovarian tumor. It does not spread to other parts of the body, and complete surgical removal is the treatment. 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 your report findings, 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. This holds even when the tumor was large, adherent, or ruptured.
Follow-up — Most cellular fibromas never come back after complete removal. A small number have recurred in the pelvis, usually years later and usually in tumors that were adherent or ruptured. For that reason, your team may suggest a period of clinical review and imaging.
Symptoms settling — If the tumor caused ascites or fluid around the lung, that fluid clears after the tumor is removed and does not require separate treatment.
Fertility — Removing one ovary does not usually prevent future pregnancy, since the other ovary continues to work. Your team can explain what your surgery means for you.
Testing for Gorlin syndrome — If tumors involved both ovaries, formed multiple nodules, or occurred at a young age, your doctor may discuss referral for genetic assessment. This matters for blood relatives as well as for you.

Your doctor will tell you what follow-up, if any, is recommended in your situation.

Questions to ask your doctor

Was the diagnosis a cellular fibroma rather than a mitotically active cellular fibroma?
How many dividing cells were counted in my tumor?
Was there any concern that the tumor could be a fibrosarcoma?
Did the tumor cells show any abnormal features under the microscope?
How large was the tumor?
Was the tumor in one ovary only, or were both ovaries involved?
Was the tumor stuck to nearby tissue, or did it rupture during surgery?
Was the ovary removed, or only the tumor?
Should I be assessed for Gorlin syndrome, and does this affect my family?
My report mentions necrosis. Does that mean anything worrying?
Were special stains or genetic testing performed, and what did they show?
What follow-up do you recommend, and for how long?
What symptoms should prompt me to contact you?