Cemento-Ossifying Fibroma (COF): Understanding Your Pathology Report

by Jason Wasserman MD PhD FRCPC
May 4, 2026

A cemento-ossifying fibroma (COF) is a noncancerous tumor that develops within the bones of the jaw, most often the mandible (lower jaw), and most often near the molar and premolar teeth. It is made up of fibrous tissue mixed with hard tissue that resembles either bone or cementum (the thin layer of mineralized tissue that normally covers the root of a tooth). Pathologists group lesions like this under the broader heading of “fibro-osseous lesions of the jaws” because they all share the same basic mix of fibrous and bone-like tissue. Cemento-ossifying fibroma is considered a true benign tumor — unlike fibrous dysplasia or cemento-osseous dysplasia, which are developmental conditions in which bone forms abnormally rather than truly growing as a mass.

Cemento-ossifying fibroma is most common in adults aged 20 to 40 and occurs roughly three to four times more often in women than in men. It tends to grow slowly over months to years and is often discovered as a painless swelling along the jaw, or by chance on a dental X-ray taken for another reason.

This article will help you understand the findings in your pathology report — what each term means and why it matters for your care.

A note on the name

The naming of this tumor has changed over the years, and you may encounter different terms in older reports:

Cemento-ossifying fibroma — The current World Health Organization (WHO) name for the classic form that arises in the tooth-bearing parts of the jaws. This is the term used in 2022 and is by far the most common form.
Ossifying fibroma — An older term still used by some pathologists. When this term is used for a tumor of the jaw, it usually refers to the same lesion.
Cementifying fibroma — A historical term, no longer in use, that emphasized the cementum-like component of the tumor.

The WHO also recognizes two related but distinct tumors under the broader heading of ossifying fibroma — juvenile trabecular ossifying fibroma and psammomatoid ossifying fibroma. These are described briefly later in the article. They behave differently and are treated differently from classic cemento-ossifying fibroma, so the specific name in your pathology report matters.

What causes cemento-ossifying fibroma?

The cause of cemento-ossifying fibroma is not known in most cases. It is not linked to smoking, alcohol, dental hygiene, or any environmental exposure that has been clearly identified. The tumor is believed to arise from the periodontal ligament — the thin layer of connective tissue that anchors each tooth to the surrounding bone. Cells in this ligament can form both bone and cementum, which explains why the tumor contains a mixture of these two materials.

A small number of patients have a rare inherited form called familial gigantiform cementoma, which is described in its own section below. The great majority of cemento-ossifying fibromas are sporadic — meaning they arise out of nowhere and are not inherited or passed on to children.

What are the symptoms of cemento-ossifying fibroma?

Many cemento-ossifying fibromas cause no symptoms in the early stages and are discovered by chance on a routine dental X-ray. As the tumor grows, it slowly expands the surrounding bone and can produce:

Swelling — A firm, painless bulge along the jaw is the most common finding.
Facial asymmetry — One side of the jaw may look visibly fuller than the other.
Tooth displacement — The tumor pushes on the roots of nearby teeth, sometimes shifting them out of position. The roots themselves can be partially eroded by the slowly growing mass.
Changes in the bite — Teeth no longer line up the way they used to.
Loose teeth — Larger tumors can erode the bone supporting the roots of nearby teeth.
Numbness — Very large tumors can press on the nerve that supplies sensation to the lower lip and chin, causing numbness or tingling.
Pain — Uncommon in cemento-ossifying fibroma, and usually only present if the tumor has become very large or has thinned the bone substantially.

How is the diagnosis made?

The diagnosis is made after a tissue sample is examined under the microscope by a pathologist. A cemento-ossifying fibroma is usually first suspected on a dental X-ray, panoramic X-ray, or cone-beam CT, which shows a well-defined, round or oval lesion within the bone of the jaw. The classic appearance is a mixed dark (radiolucent) and white (radiopaque) mass with a sharp border — sometimes with a thin clear (radiolucent) rim around the edge. As the tumor matures, it tends to become more uniformly white on imaging because more bone and cementum-like material accumulates within it. The sharp border is one of the most important features that distinguishes a cemento-ossifying fibroma from fibrous dysplasia, which has poorly defined edges and merges into the surrounding normal bone. To confirm the diagnosis, an oral and maxillofacial surgeon performs a biopsy or removes the entire tumor in a single operation. The tissue is then sent to the laboratory.

Under the microscope, the pathologist looks for a mass made up of two main components. The first is a fibrous (scar-like) stroma containing spindle-shaped cells (fibroblasts) and thin collagenous strands. The second is mineralized material — a mix of bone trabeculae (small bars of bone) and ovoid, droplet-shaped calcifications that resemble cementum. The mix of these two types of mineralized material is the histologic signature of cemento-ossifying fibroma. The tumor is well-defined and often surrounded by a thin fibrous capsule that separates it from the normal bone, a key microscopic feature that distinguishes it from fibrous dysplasia. Once the diagnosis is confirmed, no additional testing is usually needed in adults with a typical isolated tumor.

Cemento-ossifying fibroma versus fibrous dysplasia

The most important condition that cemento-ossifying fibroma must be distinguished from is fibrous dysplasia, a developmental disorder in which a portion of normal bone is gradually replaced by abnormal fibrous and bone tissue. Although both can appear as mixed dark-and-white lesions on imaging and both contain a mixture of fibrous tissue and bone under the microscope, they behave very differently and are managed very differently.

Cemento-ossifying fibroma is a true tumor with a sharp border. It can be removed cleanly from the surrounding bone, and complete removal is curative. Fibrous dysplasia, by contrast, is not a true tumor; it is a developmental abnormality of normal bone formation, has no clear border, and merges gradually into the surrounding bone. It cannot be removed cleanly, and surgery is usually limited to reshaping the affected bone for cosmetic or functional reasons rather than to complete excision. Fibrous dysplasia is also driven by a specific genetic change in the GNAS gene that is not present in cemento-ossifying fibroma. The distinction between these two diagnoses, therefore, has major implications for treatment, and your pathologist will examine the tumor carefully — often with the help of imaging — to make sure the right diagnosis is reached.

Other types of ossifying fibroma

The WHO classification recognizes two related types of ossifying fibroma that occur in younger patients and behave more aggressively than classic cemento-ossifying fibroma. They share some microscopic features but are considered separate diagnoses.

Juvenile trabecular ossifying fibroma — Most often diagnosed in children and teenagers, typically before age 15. Usually arises in the jaws. It tends to grow rapidly and recurs more often after surgery (recurrence rates of 30–60% have been reported), so it is treated more aggressively than the classic form.
Psammomatoid ossifying fibroma — Most often arises in the bones of the orbit and the sinuses (rather than in the tooth-bearing parts of the jaw). It contains small, round, layered calcifications called psammoma bodies. Until recently, it was called “juvenile psammomatoid ossifying fibroma,” but the word “juvenile” was dropped from its name in 2022 because the tumor occurs across a wide age range. Like the trabecular type, it tends to recur more often than classic cemento-ossifying fibroma.

If your pathology report uses one of these terms instead of “cemento-ossifying fibroma,” your treatment plan and follow-up schedule will be more intensive than the schedule outlined later in this article.

Familial gigantiform cementoma

Familial gigantiform cementoma is a very rare inherited condition caused by mutations in a gene called ANO5. People with this condition develop multiple, large fibro-osseous tumors of the jaws starting in childhood or early adulthood. The lesions can grow to a substantial size and cause significant facial deformity. Because the condition is inherited, family members may also be affected, and referral to a medical geneticist or genetic counselor is recommended when this diagnosis is suspected. A single isolated cemento-ossifying fibroma in an adult with no family history is not part of this condition.

Peripheral ossifying fibroma — a different diagnosis

An important distinction your pathologist must make is between cemento-ossifying fibroma (which arises within the bone of the jaw) and the peripheral ossifying fibroma (which arises in the gum tissue overlying the bone). Despite the similar name, the two are fundamentally different. The peripheral ossifying fibroma is a reactive growth — a response to chronic local irritation from things like dental plaque, calculus, ill-fitting dental appliances, or rough fillings — rather than a true tumor. It looks like a small, firm, sometimes ulcerated bump on the gum and is treated by simple removal along with cleaning of any underlying source of irritation. If your pathology report uses the term “peripheral ossifying fibroma” or “peripheral cemento-ossifying fibroma,” you have a different and considerably less worrisome diagnosis than central cemento-ossifying fibroma.

What is the prognosis?

The outlook for classic cemento-ossifying fibroma is excellent. It is benign, does not turn into cancer, and is curable by complete surgical removal. Recurrence is uncommon when the tumor has been completely removed because the well-defined capsule allows the surgeon to shell the tumor out cleanly from the surrounding bone. Recurrence rates are higher for the juvenile trabecular and psammomatoid types, which is why these variants are followed more closely. Long-term follow-up imaging is recommended for all patients to confirm bone healing and to monitor for the rare possibility of regrowth.

What happens after the diagnosis?

Treatment is led by an oral and maxillofacial surgeon, often working with a head and neck reconstructive surgeon and a dentist or prosthodontist for any later dental rehabilitation. The mainstay of treatment is surgery, and the goal is to remove the entire tumor cleanly from the surrounding bone.

Enucleation — The standard treatment for most cemento-ossifying fibromas. The tumor is shelled out of the bone in one piece, taking advantage of its well-defined capsule. The empty space fills in with new bone over several months.
Enucleation with peripheral ostectomy — A thin layer of surrounding bone is also removed when the tumor is large or when the surgeon is concerned that small fragments may be left behind. Often used for the juvenile trabecular and psammomatoid types.
Segmental resection — Removing a larger portion of the jawbone, usually with reconstruction. Reserved for very large tumors, recurrent tumors, or tumors that have substantially destroyed the jaw.
Reconstruction — When a large portion of the jaw is removed, the surgeon may rebuild it using bone from another part of the body (commonly the fibula in the lower leg) along with dental implants once the bone has healed.

After surgery, regular clinical examinations and panoramic X-rays or CT scans are performed for several years to confirm that the bone has healed and to watch for recurrence. Dental rehabilitation — including replacement of any teeth lost during surgery — can usually be planned once the bone has filled in.

Questions to ask your doctor

Which type of ossifying fibroma do I have — classic cemento-ossifying fibroma, juvenile trabecular, or psammomatoid?
Where exactly was the tumor located, and how large was it?
Was the entire tumor removed?
Were the surgical margins clear?
How was the tumor distinguished from fibrous dysplasia?
What is my estimated risk of the tumor coming back?
What is the schedule for follow-up imaging, and how long will it continue?
If teeth were removed, what are my options for replacing them?
Will I need any jaw reconstruction, and what does that involve?
Will I have any lasting numbness, changes in my bite, or changes in my facial appearance?
Are there any inherited or genetic conditions I should be evaluated for, particularly if other family members have had similar tumors?