Ovarian Fibroma: The Benign Tumor That Looks Like Cancer

An ovarian fibroma is a benign solid tumor that grows from the connective tissue of the ovary, and it is the most common tumor of its kind. 

A fibroma on the ovary can look alarming on a scan, push your CA-125 into abnormal territory, and land you in a specialist’s office before anyone can tell you what you’re actually dealing with.

Here’s what the research actually says about ovarian fibromas, including the questions people search for: how fast they grow, whether they can turn into cancer, and what happens next.

What Is an Ovarian Fibroma?

An ovarian fibroma is a benign sex cord-stromal tumor made of spindle-shaped fibroblastic cells packed into collagen. In plainer terms, it grows from the structural tissue of the ovary rather than from the egg-producing cells or the surface lining.

Fibromas account for roughly 4% of all ovarian tumors, making them the most common ovarian stromal tumor and the most common solid benign ovarian tumor. 

A few defining characteristics:

• Average age at diagnosis is 48, and fibromas are uncommon before age 30
• More than 90% are one-sided, affecting a single ovary
• Average size is about 6 cm, though the documented range runs from 1 cm to more than 21 cm
• Cystic degeneration shows up in about 25% of cases, and calcifications in about 10%

Fibromas sit on a spectrum with two close relatives. A thecoma is made of theca cells, the same cells that wrap around a developing egg follicle and help produce estrogen. 

Because of that job, thecomas are often hormonally active. A fibrothecoma has features of both. Pathologists group them together because they behave similarly, though fibrothecomas enhance more strongly on contrast imaging than pure fibromas do.

If you want the broader context for how your ovaries are built and what the surrounding tissue actually does, read our guide to ovary function.  

What Causes a Fibroma on the Ovary?

No one really knows what causes fibroma on the ovary for most women. And that’s a frustrating answer when you want a reason.

Here’s what researchers do understand. Every cell in your ovary carries a set of instructions written in DNA. Sometimes a single cell in the ovary’s structural tissue picks up an error while copying those instructions, and that error switches off the signal telling it when to stop multiplying. The cell keeps dividing. Over months or years, that becomes a fibroma.

These errors are almost always sporadic, meaning they happened in one cell during your lifetime rather than being passed down from a parent. Nothing you ate, avoided, took, or didn’t take caused it.

Scientists have identified a few of the specific errors involved:

• Extra chromosomes. Some fibromas carry three or four copies of chromosome 12 instead of the usual two. Extra copies mean extra growth instructions.
• Missing genetic backups. We inherit two copies of most genes, so one can cover if the other fails. Cellular fibromas often show a lost copy at two locations, 9q22.3 and 19p13.3. The first of those holds PTCH1, a gene whose normal job is putting the brakes on cell growth. 

That PTCH1 detail connects to the one situation where a fibroma is genuinely inherited.

Fibromas occur in roughly 25% of people with nevoid basal cell carcinoma syndrome, better known as Gorlin syndrome, which is caused by inherited mutations in that same PTCH1 gene. Gorlin-associated fibromas look different from the usual kind. They tend to affect both ovaries, appear multinodular and calcified on imaging, and show up well before age 30, sometimes in children.

So if you’re young and your scan shows fibromas on both ovaries, that’s a real reason to ask your doctor about genetic testing.

For comparison, the far more common fluid-filled sacs on the ovary form through an entirely different process. (We break that down in our article about what causes ovarian cysts.)

Symptoms Most Women Notice (and the Ones Most Women Don’t)

Small fibromas are usually silent. They’re frequently found by accident during a routine pelvic exam or an ultrasound ordered for something else entirely.

Larger ones start making themselves known through pressure rather than pain. Reported symptoms include:

• Abdominal or pelvic pain, often low-grade and persistent
• Abdominal distension or a feeling of fullness
• Increased urinary frequency
• A palpable firm mass

In a study of 23 women with ovarian fibroma, every single patient was symptomatic, and abdominal pain was universal. A firm mass was detectable on bimanual examination in 87% of them. 

Fibromas can also trigger ovarian torsion, where the mass twists and cuts off its own blood supply. That one is a surgical emergency, and it presents as sudden, severe pelvic pain.

Because bloating and pelvic pressure overlap so heavily with ovarian cancer symptoms, it’s worth knowing where the lines are. Our guide to ovarian cancer bloating explains what deserves a second look.

Meigs Syndrome: Fluid That Mimics Cancer

Some fibromas produce fluid, and this is where things get confusing for everyone involved.

Meigs syndrome is the triad of a benign ovarian tumor, ascites, and pleural effusion. It occurs in roughly 1% of ovarian fibroma cases overall, though rates run higher in surgical case series. In the 23-case study above, ascites was clinically detectable in 43.4% of patients, and two women (8.7%) met full criteria for Meigs syndrome.

The fluid resolves after the tumor comes out. But before surgery, a solid pelvic mass plus abdominal fluid plus an elevated CA-125 looks very much like advanced ovarian cancer.

How Fast Do Ovarian Fibromas Grow?

This is one of the most searched questions about fibromas, and the honest answer is that the medical literature does not publish a standard growth rate.

What the evidence does support: ordinary ovarian fibromas are slow-growing. Many women live with one for years without knowing. That’s why conservative management with periodic ultrasound is a legitimate option when the diagnosis is confident.

But growth isn’t uniform across every fibroma. In one case, a 44-year-old woman was monitored for what appeared to be a fibroid-like lesion, and follow-up imaging a year later showed a tumor that had grown to 11 cm. Pathology identified it as a mitotically active cellular fibroma.  

The practical takeaway matters more than any number. Rapid growth is the signal, not the size. A stable 7 cm mass and a 7 cm mass that doubled in eight months warrant very different conversations. If you’re on a watch-and-wait plan, the interval scans are not busywork; they’re the entire point.

Can an Ovarian Fibroma Be Cancerous?

Short answer: a true ovarian fibroma is benign and stays benign. But the fibroma family includes two entities that complicate that sentence, and you deserve to understand both.

Cellular Fibroma and Mitotically Active Cellular Fibroma

Cellular fibromas make up about 10% of all ovarian fibromas. They’re densely packed with cells, show mild atypia, and carry what pathologists call uncertain malignant potential.

When a cellular fibroma shows four or more mitoses per 10 high-power fields, it’s classified as a mitotically active cellular fibroma. These are still benign. 

They can, however, recur, particularly when the tumor ruptured during surgery, involved the ovarian surface, or had adhesions to surrounding tissue. One documented case recurred 16 years after the original operation, which is why long-term follow-up is recommended for this subtype.

Ovarian Fibrosarcoma

Ovarian fibrosarcoma is the malignant counterpart, and it is genuinely rare. Reported incidence of ovarian sarcoma overall is about 0.22 per 100,000 women. 

Distinguishing a mitotically active cellular fibroma from a fibrosarcoma comes down to pathology, not imaging. Mitotic count alone isn’t enough. Fibrosarcoma requires significant cytologic atypia alongside high mitotic activity. That distinction protects women from overtreatment, especially young women who want to preserve fertility.

This is the same diagnostic problem that shows up across ovarian tumors generally. If you’re sorting through your own results, our guides on benign vs malignant ovarian tumor and ovarian cyst vs tumor both go deeper.

How Doctors Diagnose an Ovarian Fibroma

Preoperative diagnosis is difficult. Not because doctors aren’t paying attention, but because fibromas are excellent impersonators.

Transvaginal ultrasound is the first-line imaging test. Fibromas typically appear as solid, hypoechoic masses with posterior acoustic shadowing and minimal blood flow on Doppler. The problem is that this description also fits a pedunculated uterine fibroid almost exactly.

MRI is where the picture usually sharpens, and it works because of what fibromas are made of. Dense, packed collagen shows up dark on certain MRI settings, while most cancerous tissue shows up bright. That contrast alone rules a lot of things out.

The second clue is how the tumor responds to contrast dye. During an MRI, dye is injected into a vein and radiologists watch how quickly and how brightly different tissues light up. Tumors with heavy blood supply light up fast. Fibromas, which are mostly dense fiber and not many blood vessels, light up weakly and slowly.

That difference is measurable, and it turns out to be useful for a problem that trips up a lot of scans: telling an ovarian fibroma apart from a uterine fibroid. The two can look nearly identical otherwise.

In one study, researchers found that when a mass lit up faintly with contrast dye, it was a fibroma or fibrothecoma about 92% of the time. Uterine fibroids lit up noticeably brighter.

The same study found something reassuring about larger fibromas. Once a fibroma passes about 6 cm, it commonly develops a visible rim around it, patchy areas inside where tissue has broken down or filled with fluid, and an uneven, mottled appearance overall.

On a radiology report, that can read like bad news. It usually isn’t. Those changes track with size, not with cancer. A big fibroma simply outgrows parts of its own blood supply, and the tissue inside starts to degrade. It’s the tumor aging, not turning.

Worth asking your radiologist or gynecologist directly: does this mass look uneven because it’s large, or because of something else?

CA-125 is the least reliable piece of the puzzle. It’s a protein in your blood that often runs high in ovarian cancer, so doctors measure it when a mass turns up. But plenty of harmless things raise it, too: a large mass pressing on your abdominal lining, fluid buildup, endometriosis, even your period.

In the 23-woman study, CA-125 was elevated in 61% of patients. All of them had a benign fibroma, and levels returned to normal after surgery. An abnormal result is a reason to keep looking, not a diagnosis.  

A frozen section usually settles it. During surgery, a piece of the removed mass goes straight to a pathologist, who freezes it, slices it, and examines it under a microscope within about 30 minutes. If it’s benign, the surgeon stops there. If it isn’t, the operation expands to full cancer staging. In that same study, the frozen section result matched the final pathology in 22 of 23 cases.

Not every hospital offers it, so it’s worth asking before your surgery date.

Treatment: Surgery Isn’t Always the Answer

Treatment depends on certainty, size, symptoms, age, and whether you want children.

When imaging clearly points to a benign fibroma and you have no symptoms, observation with scheduled ultrasounds is reasonable. When the diagnosis is uncertain, the mass is large, symptoms are interfering with your life, or Meigs syndrome is present, surgery is recommended.

The surgical options scale with the situation:

• Ovarian cystectomy or tumor excision, preserving the ovary, in younger patients.
• Unilateral salpingo-oophorectomy, removing one ovary and tube, which remains fertility-sparing. 
• Hysterectomy with bilateral salpingo-oophorectomy, generally reserved for postmenopausal women or those who have completed their families.

Ask whether laparoscopic removal with a retrieval bag is possible. Containing the specimen prevents spillage into the abdominal cavity, and spillage is one of the documented risk factors for recurrence in cellular fibromas.

What Your Prognosis Actually Looks Like

Excellent. For conventional ovarian fibromas, surgical removal is curative, and recurrence is rare. Meigs syndrome resolves once the tumor is out. CA-125 normalizes. Most women return to routine gynecologic care.

Cellular and mitotically active cellular fibromas need longer surveillance, especially after rupture, surface involvement, or adhesions. That’s monitoring, not treatment.

Questions Worth Asking Your Doctor

Bring these to your appointment:

• Does my imaging suggest a fibroma, a fibrothecoma, or something less certain?
• Is observation with repeat ultrasound an option, and how often would we scan?
• Will a frozen section be performed during surgery?
• Can this be done laparoscopically with a retrieval bag?
• Can we preserve my ovary or my fertility?
• If pathology shows a cellular fibroma, what does follow-up look like?

If your mass is large, your CA-125 is elevated, imaging is indeterminate, or anyone has used the word “suspicious,” ask for a referral to a gynecologic oncologist. These specialists manage complex adnexal masses constantly and are best positioned to distinguish a benign fibroma from something that needs cancer-level care.

What to Remember If You’re Facing an Ovarian Mass

An ovarian fibroma is benign, and for most women, surgery is the end of the story. It’s the waiting that wears people down. Imaging can’t always tell a fibroma from a uterine fibroid. CA-125 can climb for reasons that have nothing to do with cancer. And a definitive answer often comes only after the tissue is out and under a microscope.

So make the waiting count. Ask whether your imaging points to a fibroma or something less certain. Ask whether a frozen section will be done during surgery. 

If anyone has called your mass “suspicious,” ask for a referral to a gynecologic oncologist, and use our guide to find a gynecologic oncologist to choose one with the right experience. If the picture still feels unclear, an ovarian cancer second opinion is a reasonable next step, not an insult to your doctor.

A fibroma can look alarming long before anyone knows what it is. Once you have the answer, it’s usually a manageable one.