Ameloblastoma: Understanding Your Pathology Report

by Jason Wasserman MD PhD FRCPC
April 30, 2026

Ameloblastoma is a noncancerous tumor that arises in the bones of the jaw. It develops from cells normally involved in tooth formation (the words “odonto” and “genic” mean “tooth-producing”), which is why pathologists describe it as an odontogenic tumor. Ameloblastomas typically grow slowly over many years. Small tumors often cause no symptoms, but as they enlarge, they can loosen teeth, swell the jaw, and reshape the bone enough to change a person’s facial appearance. Although ameloblastoma is benign, it is locally aggressive — it can destroy bone and recur after surgery, which is why it is taken seriously and treated like a tumor that needs to be completely removed.

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

What causes ameloblastoma?

The cause of ameloblastoma is not known in most cases. It is not linked to smoking, alcohol, infection, or any environmental exposure that has been clearly identified. What scientists have learned is that the great majority of ameloblastomas carry a specific change in their DNA — a mutation in a gene called BRAF, almost always the V600E variant. This mutation acts like a stuck accelerator in a signaling pathway that tells cells to grow and divide, and it is present in roughly two-thirds of ameloblastomas arising in the lower jaw. A smaller number of ameloblastomas, particularly those in the upper jaw, carry a different mutation in a gene called SMO. These mutations occur by chance during a person’s lifetime; they are not inherited and cannot be passed to children.

Where does ameloblastoma start?

Most ameloblastomas start in the jaw. The jaw is made up of two bones — the mandible (the lower jaw) and the maxilla (the upper jaw). About 80% of ameloblastomas arise in the mandible, most often near the back of the lower jaw where the molars and wisdom teeth are located. The remaining 20% arise in the maxilla. A rare form called peripheral (or extraosseous) ameloblastoma develops in the gum tissue overlying the jaw rather than within the bone itself.

Teeth develop within the mandible and maxilla before birth, although they do not erupt until months or years later. Each tooth grows from a structure called the tooth bud, which contains specialized cells called ameloblasts that produce enamel — the hard outer surface of the tooth. After the teeth have finished forming, small clusters of ameloblasts can remain trapped in the jawbone. Ameloblastoma is thought to arise from these leftover cells.

What are the symptoms of ameloblastoma?

Small ameloblastomas usually cause no symptoms and are often found by chance on a dental X-ray taken for another reason. As the tumor grows, it expands the bone of the jaw and can produce:

Swelling — A firm, painless bulge along the jaw is the most common finding.
Loose or displaced teeth — The tumor pushes on the roots of nearby teeth.
Changes in the bite — Teeth no longer line up the way they used to.
Facial asymmetry — One side of the jaw looks visibly larger than the other.
Numbness — Larger tumors can press on the nerve that supplies sensation to the lower lip and chin.
Pain or jaw fracture — Uncommon, but possible if the tumor 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. Most patients first have an imaging study — usually a panoramic dental X-ray, often followed by a CT scan or MRI — that shows a clear or partially clouded space in the jawbone. Imaging cannot make the diagnosis on its own because several other jaw lesions can look similar, including odontogenic cysts and other odontogenic tumors. To confirm the diagnosis, an oral and maxillofacial surgeon performs a biopsy, in which a small sample of the abnormal tissue is removed through the mouth or, less commonly, through a small opening in the bone. In some cases, the entire tumor is removed in one operation, and the diagnosis is made on the resection specimen rather than on a separate biopsy.

Under the microscope, the pathologist looks for groups of cells called nests or follicles that closely resemble the ameloblasts of the developing tooth. The cells at the edge of each nest line up side-by-side in a regimented row — a pattern called peripheral palisading — and the nucleus (the part of the cell that holds its DNA) sits at the top of the cell rather than the bottom. This unusual upside-down arrangement is described as reverse polarity and is one of the most reliable clues to the diagnosis. The cells in the center of each nest are loose and stellate (star-shaped), resembling a structure in the developing tooth called the stellate reticulum. Once the diagnosis is confirmed, imaging is used to map the full extent of the tumor and to plan the operation that will remove it.

Variants of ameloblastoma

The 2022 World Health Organization classification recognizes several distinct types of ameloblastoma. These categories matter because they behave differently and are treated differently.

Conventional ameloblastoma — The most common type. It grows as a solid or partly cystic mass within the jawbone. This type carries the highest risk of recurrence and is usually treated with complete surgical removal, including a margin of normal bone.
Unicystic ameloblastoma — A single fluid-filled cyst lined by ameloblastoma cells. It tends to occur in younger patients and has a lower recurrence rate than the conventional type, particularly when the tumor is confined to the cyst lining and has not invaded the surrounding bone.
Peripheral (extraosseous) ameloblastoma — A rare form that arises in the gum tissue rather than within the bone. It behaves less aggressively than tumors within the jaw and is usually cured by complete local excision.
Metastasizing ameloblastoma — A very rare situation in which a histologically benign-looking ameloblastoma spreads, most often to the lungs. The microscopic appearance is identical to that of conventional ameloblastoma, but the tumor has somehow escaped the jaw and seeded elsewhere. Despite the spread, it is still considered a separate entity from ameloblastic carcinoma (the truly malignant counterpart described below).

Microscopic patterns within conventional ameloblastoma

Within conventional ameloblastoma, pathologists describe several microscopic growth patterns. These descriptions describe how the tumor cells are arranged but do not change the diagnosis or the recommended treatment.

Follicular pattern — The most common pattern. The tumor grows as round nests of cells that resemble the developing tooth bud, with peripheral palisading and stellate reticulum-like cells in the center.
Plexiform pattern — The tumor cells form long, branching cords or chains rather than discrete round nests. Pathologists describe these chains as anastomosing (joined together).
Desmoplastic pattern — The tumor nests are small and are surrounded by dense, scar-like connective tissue (the word “desmoplastic” means “fibrous-tissue-forming”). This pattern is more often seen in the upper jaw.
Acanthomatous pattern — The cells in the center of the tumor nests have transformed into squamous (skin-like) cells, sometimes with keratin formation. The peripheral palisading and reverse polarity at the edges of the nests confirm that this is still ameloblastoma rather than a squamous tumor.
Granular cell pattern — The cells in the center of the nests have a pink, grainy-looking interior. This pattern is uncommon and does not change behavior.
Basal cell pattern — The tumor is composed of small, dark cells with little cytoplasm, resembling the skin’s basal cells.

It is common for two or more of these patterns to be present in the same tumor.

What about ameloblastic carcinoma?

Ameloblastic carcinoma is the malignant (cancerous) counterpart of ameloblastoma and is a separate diagnosis. It is rare. Under the microscope, ameloblastic carcinoma still shows some of the features of ameloblastoma — peripheral palisading, reverse polarity — but the cells also show clear features of cancer: marked variation in size and shape, frequent dividing cells (mitotic figures), and areas of cell death (necrosis). Unlike ameloblastoma, ameloblastic carcinoma can spread to lymph nodes and to distant sites such as the lungs. Because the treatment and prognosis are very different, the distinction between ameloblastoma and ameloblastic carcinoma must be clearly stated in your pathology report.

Surgical margins

A margin is the edge of the tissue that the surgeon cuts when removing a tumor. The pathologist examines these edges under the microscope to determine whether any tumor cells reach the cut surface. The margin status is one of the most important findings in your pathology report because it tells you and your surgeon whether the tumor was completely removed.

Negative margin — No tumor cells are seen at the cut edge. This suggests the tumor was completely removed, and the chance of it growing back is much lower.
Close margin — Tumor cells are very close to the cut edge but do not reach it. Pathologists may report the exact distance in millimeters. A close margin raises the risk that small clusters of tumor cells were left behind in nearby bone.
Positive margin — Tumor cells are seen at the cut edge of the tissue. This means tumor cells were almost certainly left behind in the body. A positive margin usually means a second operation will be needed to remove more bone, or that close follow-up imaging will be required to watch for recurrence.

Because ameloblastoma can recur even when the margin appears negative — small extensions of tumor can travel through bone beyond what is visible to the eye — most surgeons aim for a margin of at least 1 to 1.5 cm of normal bone around the tumor. This is why the operation for ameloblastoma is often more extensive than the size of the tumor on imaging would suggest.

Biomarker and molecular testing

Biomarker testing is not yet a routine part of every ameloblastoma report, but it is becoming more common, particularly for tumors that are large, recurrent, or located where complete surgical removal would cause serious functional or cosmetic harm. The two most relevant tests are described below.

BRAF V600E

The BRAF gene normally helps cells receive signals to grow and divide in a controlled way. The V600E mutation changes a single building block in the BRAF protein and locks it in the “on” position, so the cell receives a constant grow-and-divide signal even when none is needed. This mutation is found in approximately 60–70% of mandibular ameloblastomas and in a smaller proportion of maxillary ameloblastomas. Detecting it has two practical consequences. First, it can confirm an uncertain diagnosis when the microscopic findings alone are ambiguous. Second, it identifies tumors that may respond to BRAF-inhibitor drugs such as dabrafenib, often combined with the MEK inhibitor trametinib. These drugs are the same ones used to treat BRAF-mutant melanoma and lung cancer, and there are now multiple published reports of patients with unresectable or recurrent ameloblastoma whose tumors shrank substantially on BRAF-targeted therapy. Testing is performed on the tumor tissue using either immunohistochemistry (a special stain that detects the abnormal V600E protein) or DNA sequencing. The result is reported as “BRAF V600E mutation detected” or “no mutation detected.” For more information about BRAF, please see this article.

SMO

Mutations in the SMO gene activate a signaling pathway called the Hedgehog pathway, which drives growth in some ameloblastomas — particularly those in the upper jaw. SMO mutations and BRAF mutations are usually mutually exclusive, meaning a tumor has one or the other but rarely both. Tumors with SMO mutations may respond to a class of drugs called Hedgehog-pathway inhibitors (such as vismodegib), which are already approved for advanced basal cell carcinoma of the skin. The use of these drugs in ameloblastoma is still experimental. Testing for SMO mutations is done by DNA sequencing, usually as part of a larger panel of genes.

If you are interested in learning more about biomarkers and molecular testing in cancer, please see our biomarkers section.

What is the prognosis?

The overall outlook for ameloblastoma is excellent. It is a benign tumor and does not behave like cancer in most patients. The principal long-term concern is recurrence — the tumor growing back in the same area after surgery. The reported recurrence rate depends heavily on tumor type and the type of surgery performed.

Conventional ameloblastoma — Recurrence rates are reported as roughly 50–90% after simple enucleation (scooping the tumor out), but drop to under 15% after wider resection with a clear margin of normal bone.
Unicystic ameloblastoma — Recurrence rates are lower, ranging from about 10% to 25%, especially when the tumor has not invaded the surrounding bone.
Peripheral ameloblastoma — Recurrence is uncommon when the tumor is removed with a margin of normal tissue.
Metastasizing ameloblastoma — Very rare. Spread, when it occurs, most often involves the lungs and may present many years after the original diagnosis. Outcomes are usually good with surgical removal of the metastatic deposits.

Most recurrences occur within the first 5 years after surgery, but late recurrences — even more than 10 years after the original operation — are well documented. This is the reason long-term imaging follow-up is recommended.

What happens after the diagnosis?

Treatment for ameloblastoma is led by an oral and maxillofacial surgeon, often working with a head and neck reconstructive surgeon, a dentist or prosthodontist, and (in selected cases) a medical oncologist if targeted drug therapy is being considered. The mainstay of treatment is surgery, and the goal is to remove the entire tumor with a margin of normal bone around it.

Marginal or segmental resection — Removing the affected portion of the jawbone, often together with a small amount of normal bone on either side. This is the most common operation for conventional ameloblastoma.
Enucleation and curettage — Scooping out the tumor without removing the surrounding bone. This is sometimes used for small unicystic tumors but carries a higher risk of recurrence and is usually reserved for selected cases.
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.
Targeted drug therapy — For tumors that cannot be safely removed with surgery, that have come back after multiple operations, or that have spread, BRAF-inhibitor drugs are an emerging option for tumors that carry the BRAF V600E mutation.
Radiation therapy — Rarely used for ameloblastoma because the tumor is generally not very radiation-sensitive and because radiation to the jaw carries its own long-term risks. It is occasionally used for tumors that cannot be removed surgically.

After surgery, regular clinical examinations and imaging (typically a panoramic X-ray or CT scan) are performed for many years to watch for recurrence. Dental rehabilitation — including implants, bridges, or dentures — is often a long-term part of recovery, especially when a portion of the jaw has been removed.

Questions to ask your doctor

Where exactly in my jaw did the tumor start, and how large was it?
Which type of ameloblastoma do I have — conventional, unicystic, peripheral, or metastasizing?
Which microscopic pattern (follicular, plexiform, desmoplastic, acanthomatous, granular, basal) does my tumor show, and does it affect my treatment?
Was the tumor completely removed? What were the surgical margins?
If a margin was positive or close, will I need more surgery, and what will the second operation involve?
Was my tumor tested for BRAF V600E or SMO mutations? If not, would testing be appropriate in my situation?
If my tumor cannot be completely removed, am I a candidate for BRAF-inhibitor drugs?
What is my estimated risk of the tumor coming back?
What is the schedule for follow-up imaging, and how long will it continue?
What does dental and jaw reconstruction look like in my case, and when can it begin?
Will I have any lasting numbness, changes in my bite, or changes in my facial appearance?
Are there clinical trials I should consider?