Pleomorphic Adenoma: Understanding Your Pathology Report

by Jason Wasserman MD PhD FRCPC
May 8, 2026

Pleomorphic adenoma is a noncancerous tumor that starts in the salivary glands — the glands that make saliva. It is the most common salivary gland tumor of any kind, in both adults and children, and accounts for about two-thirds of all salivary gland tumors. The name “pleomorphic” means “many shapes” and refers to the mix of cell types and tissue patterns seen under the microscope in the tumor. Pleomorphic adenoma is benign — it does not spread to other parts of the body and rarely invades surrounding tissues. However, it tends to grow slowly over time, can come back after surgery if not completely removed, and very occasionally turns into a cancer if left untreated for many years. For these reasons, surgery is usually recommended.

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 pleomorphic adenoma?

The cause of pleomorphic adenoma is not known. It is not strongly linked to smoking, alcohol, or any other lifestyle factor, and it is not part of any known inherited cancer syndrome. The one weak risk factor that has been identified is previous radiation exposure to the head or neck, but most patients have no history of radiation.

Scientists have learned that most pleomorphic adenomas have a specific change in their DNA — a fusion involving one of two genes. About 70% of pleomorphic adenomas have a PLAG1 fusion, while about 10–15% have an HMGA2 fusion. A fusion happens when two genes that are normally far apart on different chromosomes break and join together. The new combined gene then turns on tumor growth signals at high levels, allowing the tumor to form. These genetic changes happen by chance during a person’s lifetime. They are not inherited and cannot be passed to children.

Where does pleomorphic adenoma start?

Pleomorphic adenoma can start in any salivary gland. About 85% of cases arise in the parotid gland, the largest salivary gland, which sits in front of and below each ear. Within the parotid gland, the tumor most often starts in the superficial lobe (the part closest to the skin) rather than the deep lobe. About 8% of cases arise in the submandibular gland (under the jaw), and the remainder arise in the small minor salivary glands distributed throughout the lining of the mouth and throat — most often in the palate (the roof of the mouth) and upper lip. Tumors arising in the sublingual gland (under the tongue) are uncommon, but tumors in this site are proportionally more likely to be cancerous than benign. Pleomorphic adenoma can also occur in the skin (where it is sometimes called a benign mixed tumor) and, rarely, in other locations, such as the upper airway.

Pleomorphic adenoma can occur at any age but is most common between 30 and 50 years old, substantially younger than most salivary gland cancers. It is slightly more common in women than in men.

What are the symptoms of pleomorphic adenoma?

Pleomorphic adenoma usually grows slowly over months to years, and many tumors are noticed by the patient or a family member long before they cause any other symptoms:

Painless lump or swelling — A firm, slow-growing, painless lump near the jaw, cheek, or ear is the most common finding by far. Tumors of the parotid gland are typically felt under the skin in front of or below the ear. Tumors of the submandibular gland are felt under the jaw. Tumors of the minor salivary glands appear as a firm bulge inside the mouth, usually on the palate.
Sensation of fullness — Some patients describe a feeling of pressure or fullness in the affected area before they can feel a definite lump.
Difficulty chewing, speaking, or swallowing — Larger tumors of the minor salivary glands or the deep parotid lobe can interfere with normal mouth function.
Sudden change in a long-standing lump — A lump that has been stable for years and then suddenly starts to grow more quickly is a warning sign that the tumor may have turned into cancer (described in the section on malignant transformation below).
Pain or facial weakness — Uncommon in pleomorphic adenoma. New pain, numbness, or weakness of the muscles of the face raises concern that the tumor is no longer benign and is one of the reasons surgery is recommended even for asymptomatic tumors.

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 test — usually an ultrasound, CT scan, or MRI — that shows a well-defined mass in the salivary gland. A fine needle aspiration biopsy (FNAB) is often done first to take a small sample of cells through a thin needle. If the FNAB does not give a clear answer, a core needle biopsy may be done instead. In many cases, the entire tumor is removed in a single operation, and the diagnosis is made on this larger sample.

Under the microscope, the pathologist looks for a tumor made up of three components — the combination that gives this tumor its name:

Epithelial cells — Cells arranged in clusters, cords, or small tube-like structures called ducts.
Myoepithelial cells — Cells that surround the epithelial component. They can take on many different shapes — spindle-shaped (long and thin), plasmacytoid (round with eccentric nuclei), or clear cell (with pale-looking cytoplasm) — within the same tumor.
Chondromyxoid stroma — A unique background tissue that is part cartilage-like and part mucus-like. It is one of the most distinctive features of pleomorphic adenoma and is rarely seen in other salivary gland tumors. The word “chondro” means cartilage, and “myxoid” means mucus-like.

In most major salivary gland tumors, a thin capsule of fibrous tissue surrounds the tumor. The capsule can be incomplete or interrupted in places, and finger-like tumor extensions (sometimes called pseudopods) can poke through the capsule into the surrounding salivary gland tissue. Tumors arising in minor salivary glands often lack a true capsule, which is why they need to be removed with a small rim of normal surrounding tissue. Pleomorphic adenoma cells show only a few mitotic figures (cells in the act of dividing), no marked variation in size and shape, and no necrosis (areas of cell death). Any of these features should prompt the pathologist to consider whether the tumor has turned into cancer.

To confirm the diagnosis, the pathologist may use immunohistochemistry, a staining technique that highlights specific proteins in tumor cells. The epithelial cells are typically positive for cytokeratins, while the myoepithelial cells are typically positive for S100, p63, smooth muscle actin, calponin, and SOX10. In cases where the diagnosis is uncertain — particularly on small biopsy samples — molecular testing for a PLAG1 or HMGA2 fusion can be helpful. The most useful tests for finding these fusions are next-generation sequencing (NGS) and fluorescence in situ hybridization (FISH).

Surgical margins

A margin is the edge of the tissue that the surgeon cuts when removing the tumor. The pathologist examines these edges under the microscope to see whether any tumor cells reach the cut surface.

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. The pathologist may report the exact distance in millimeters. A close margin can raise the risk that the tumor will come back near the original site.
Positive margin — Tumor cells are seen at the cut edge of the tissue. This means tumor cells were almost certainly left behind and the chance of recurrence is higher.

Margin assessment is particularly important in pleomorphic adenoma because the thin, sometimes incomplete tumor capsule and the tendency for finger-like extensions through the capsule can leave behind small clusters of tumor cells that grow back years or even decades later. This is the main reason surgeons remove pleomorphic adenomas with a cuff of surrounding normal salivary gland tissue, rather than simply scooping out (enucleating) the tumor.

Can a pleomorphic adenoma turn into cancer?

Yes, but this is uncommon. Over time, the cells of a pleomorphic adenoma can develop additional DNA changes that turn the tumor into a cancer — most often a salivary gland cancer called carcinoma ex pleomorphic adenoma (“ex” means “from”). The most common type of cancer to develop within a pleomorphic adenoma is salivary duct carcinoma, but other types of salivary gland cancer can also arise this way. Several factors raise the risk of malignant transformation:

Long duration — The risk increases the longer the tumor has been present. Studies have estimated the lifetime risk of malignant transformation at roughly 5–10% if a pleomorphic adenoma is left untreated for many years.
Large size — Larger tumors are more likely to harbor an area of malignant transformation than smaller tumors.
Multiple previous recurrences — Tumors that have come back several times after surgery have a higher risk of eventually turning into cancer.
Sudden change in growth, pain, or facial weakness — A pleomorphic adenoma that has been stable for years and then suddenly begins to grow rapidly, becomes painful, or causes facial weakness should be evaluated promptly because these are warning signs of malignant transformation.

This small but real risk is one of the main reasons surgery is recommended even when the tumor is not causing symptoms.

What is the prognosis?

The outlook for pleomorphic adenoma is excellent. The tumor is benign, and complete surgical removal cures most patients. Long-term survival is the same as for the general population. The principal long-term concern is recurrence — the tumor coming back in the same area after surgery — and the risk depends heavily on the type of operation performed.

Complete formal resection (parotidectomy or full gland excision) with negative margins — Recurrence is uncommon, with reported rates under 5%.
Enucleation (simply scooping the tumor out) — Historically associated with much higher recurrence rates, sometimes reported between 25% and 45%, because the thin capsule can be broken during the operation and small fragments of tumor can be left behind in the surgical bed.
Recurrent pleomorphic adenoma — When pleomorphic adenoma comes back, it often returns as multiple small nodules scattered throughout the surgical site (multinodular recurrence) rather than as a single mass. This pattern is more difficult to fully remove and may require larger or repeated operations.

Because pleomorphic adenoma can come back many years — sometimes decades — after the original surgery, long-term clinical follow-up is recommended. Some surgeons also recommend periodic imaging.

What happens after the diagnosis?

Treatment for pleomorphic adenoma is led by a head and neck surgeon. The goal of surgery is to remove the entire tumor with a rim of normal surrounding salivary gland tissue, while preserving important nearby structures — particularly the facial nerve.

Parotidectomy — The standard operation for parotid pleomorphic adenoma. Most tumors are treated with a superficial parotidectomy (removal of the part of the gland above the facial nerve). For tumors in the deep lobe of the parotid gland, a total parotidectomy may be needed. The facial nerve is preserved whenever possible.
Submandibular gland excision — The standard operation for pleomorphic adenoma of the submandibular gland. The entire gland is removed.
Wide local excision — The standard operation for pleomorphic adenoma of the minor salivary glands (such as those of the palate). The tumor is removed along with a small rim of healthy surrounding tissue.
Reconstruction — When a large amount of tissue must be removed (for example, from the palate), reconstruction with a skin graft, local tissue flap, or dental appliance may be needed.
Long-term surveillance — Regular clinical examination of the head and neck continues for many years after surgery because of the possibility of late recurrence. Imaging is sometimes added if any new changes are noticed.

Radiation therapy and chemotherapy are not used for benign pleomorphic adenoma. Radiation is used only in selected cases of multiply recurrent disease that cannot be controlled with further surgery.

Questions to ask your doctor

Where exactly was the tumor located, and how large was it?
Was the tumor completely removed? What were the surgical margins?
If a margin was positive or close, what does that mean for me, and will I need any further treatment?
Was there any sign that part of the tumor had turned into cancer?
What type of operation did I have — was it a formal resection or an enucleation?
What is my estimated risk of the tumor coming back?
What is the schedule for follow-up, and how long will it continue?
Will I have any lasting facial weakness, numbness, or dryness of the mouth from the surgery?
If the tumor comes back, what would the next steps be?
Should anyone in my family be screened for similar tumors?