Mucoepidermoid Carcinoma: Understanding Your Pathology Report

by Jason Wasserman MD PhD FRCPC
May 5, 2026

Mucoepidermoid carcinoma is a type of cancer that starts in the salivary glands — the glands that make saliva. It is the most common salivary gland cancer in both adults and children. Mucoepidermoid carcinoma can also start in less common locations, including the lungs, the lining of the sinuses, and other glands of the head and neck. The tumor is made up of three different types of cells, and the mix of those cells helps the pathologist decide the grade of the tumor — a number that strongly predicts how the cancer will behave. Most mucoepidermoid carcinomas are low or intermediate grade and have an excellent outlook after surgery. A smaller number are high grade and are treated more aggressively.

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 mucoepidermoid carcinoma?

The cause of mucoepidermoid carcinoma is not known in most cases. It is not strongly linked to smoking, alcohol, or any other lifestyle factor. The one well-recognized risk factor is previous radiation therapy to the head or neck — for example, radiation given in childhood for Hodgkin lymphoma or another cancer. Mucoepidermoid carcinoma is the most common salivary gland cancer to develop years after radiation treatment.

Scientists have learned that most mucoepidermoid carcinomas have a specific change in their DNA. The most common change is a fusion involving a gene called MAML2. A fusion happens when two genes that are normally far apart on different chromosomes break and join together. The new combined gene then behaves abnormally. The most common partner gene is CRTC1, and a smaller number of tumors have a fusion involving a related gene, CRTC3. The fusion creates an abnormal protein that drives the tumor cells to keep dividing. The fusion is most common in low- and intermediate-grade tumors and far less common in high-grade tumors. This genetic change happens by chance during a person’s lifetime. It is not inherited and cannot be passed to children.

Where does mucoepidermoid carcinoma start?

Mucoepidermoid carcinoma can start in any salivary gland. About half of all cases arise in the parotid gland, which sits in front of and just below each ear. The next most common site is the small minor salivary glands distributed throughout the lining of the mouth and throat, particularly the palate (the roof of the mouth). The remainder occur in the submandibular gland (under the jaw) or, less commonly, the sublingual gland (under the tongue).

Mucoepidermoid carcinoma can occur at any age but is most common between 30 and 50 years old. It is slightly more common in women than in men. It is the most common salivary gland cancer in children and the most common salivary cancer to arise in patients who received radiation therapy to the head or neck many years earlier.

What are the symptoms of mucoepidermoid carcinoma?

The symptoms depend on where the tumor is located and how aggressive it is:

Painless lump or swelling — A slow-growing, painless mass in the salivary gland is the most common finding. In the parotid gland, the lump is felt under the skin in front of or below the ear. In a minor salivary gland, it appears as a firm bulge inside the mouth, sometimes with a thinning or sore on the surface.
Pain or tenderness — Uncommon in low-grade tumors. New pain may be a warning sign that the tumor is high grade or has invaded a nerve.
Numbness or facial weakness — The facial nerve runs through the parotid gland. Tumors that press on or invade this nerve can cause weakness or paralysis of part of the face. This is much more common with high-grade tumors.
Difficulty swallowing or opening the mouth — Larger tumors of the minor salivary glands or palate can interfere with normal mouth function.
Swelling in the neck — Sometimes caused by spread of the tumor to nearby lymph nodes. This is also more common with high-grade 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 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 different types of cells, which is one of the defining features of mucoepidermoid carcinoma:

Mucous cells — Large cells filled with a fluid called mucin. These cells appear pale or blue under the microscope and are sometimes called goblet cells because of their shape. They line small fluid-filled spaces called cysts.
Epidermoid cells — Pink-staining cells that look similar to the squamous cells of the skin. They tend to grow in solid sheets or nests.
Intermediate cells — Smaller cells that share features of the other two types. They are often the most numerous cell type, particularly in low-grade tumors.

The mix of these three cell types varies from tumor to tumor and is the basis of the grading system described in the next section. In some cases, the pathologist also orders molecular testing to confirm the diagnosis. Most mucoepidermoid carcinomas have a MAML2 fusion, as described in the “What causes” section. The fusion can be detected directly using techniques such as fluorescence in situ hybridization (FISH) or next-generation sequencing (NGS). Molecular testing is most useful when microscopic features are atypical, when the tumor has unusual variants (such as sclerosing, oncocytic, clear cell, or Warthin-like variants), or when the diagnosis needs to be confirmed in a small biopsy sample. Once the diagnosis is confirmed, additional imaging is used to assess spread before treatment is planned.

Histologic grade

The histologic grade is the most important finding in any pathology report for mucoepidermoid carcinoma. Grade describes how aggressive the tumor appears under the microscope and strongly predicts how the cancer is likely to behave. Grade is also the main factor that decides treatment — low-grade tumors are usually treated by surgery alone, while higher-grade tumors usually need radiation therapy after surgery.

Pathologists use a three-tier system: low grade, intermediate grade, or high grade. The most widely used grading system is one originally developed by the Armed Forces Institute of Pathology (AFIP) in the United States. A second system, developed by Brandwein, includes a few additional features. Many pathologists today use a hybrid of the two. In both systems, the pathologist checks for a list of specific microscopic features and assigns points based on which features are present.

AFIP grading features

Cysts — Most mucoepidermoid carcinomas contain fluid-filled spaces lined by tumor cells. A tumor in which less than 20% of the area is made up of cysts is given 2 points (more solid tumors are usually more aggressive).
Necrosis — Necrosis is an area of cell death within the tumor. A tumor with necrosis is given 3 points.
Perineural invasion — Tumor cells growing around or along a nerve. A tumor with perineural invasion is given 2 points.
Anaplasia — Tumor cells that look very abnormal compared with normal cells. A tumor with anaplasia is given 4 points.
Mitoses — Tumor cells that are actively dividing. A tumor with more than 4 mitotic figures in a defined area is given 3 points.

The total points add up to the final grade:

Low grade — 0 to 4 points.
Intermediate grade — 5 or 6 points.
High grade — 7 or more points.

Brandwein features

The Brandwein system adds three further features to the scoring:

Pattern of growth — A tumor that grows mainly as solid sheets or large nests of cells (rather than as cysts) is given 2 points.
Lymphovascular invasion — Tumor cells inside small blood vessels or lymphatic vessels. A tumor with lymphovascular invasion is given 3 points.
Bone invasion — Tumor cells that have invaded nearby bone. A tumor with bone invasion is given 3 points.

Whichever system is used, the grade is reported as low, intermediate, or high — and that single word is the most important predictor of how the cancer is likely to behave.

Tumor extension (extraparenchymal extension)

Extraparenchymal extension means the tumor has spread beyond the salivary gland into surrounding tissues, such as fat, muscle, or skin. This finding is reported only for tumors that arise in one of the three major salivary glands — the parotid, submandibular, or sublingual gland. Tumors with extraparenchymal extension are given a higher pathologic stage (pT) and are at higher risk of coming back after surgery.

Lymphovascular invasion

Lymphovascular invasion means that tumor cells have entered small blood vessels or lymphatic vessels in or near the tumor. These vessels can carry the cells to lymph nodes or to distant parts of the body. Lymphovascular invasion is uncommon in low-grade mucoepidermoid carcinoma and much more common in high-grade tumors. When found, it raises the risk that the cancer will come back, and it may influence the decision to recommend radiation therapy after surgery.

Perineural invasion

Perineural invasion means that tumor cells are growing around or along a nerve. The facial nerve, which controls the muscles of facial expression, runs through the parotid gland and is the most common nerve involved when mucoepidermoid carcinoma starts there. Perineural invasion can cause new pain, numbness, or facial weakness. When seen on a pathology report, it raises the risk that the tumor will come back near the original site, and your doctor may recommend radiation therapy after surgery to lower that risk.

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, and may lead to a recommendation for radiation therapy after surgery.
Positive margin — Tumor cells are seen at the cut edge of the tissue. This means tumor cells were almost certainly left behind. A positive margin usually leads to a recommendation for either more surgery or radiation therapy after surgery.

Margin assessment is especially difficult in parotid surgery because the surgeon must work around the facial nerve. For this reason, close margins are common even when the surgery has been carefully performed.

Lymph nodes

Lymph nodes are small immune organs scattered throughout the body. The lymph nodes most likely to be involved by mucoepidermoid carcinoma are those in the neck. During surgery, lymph nodes near the tumor may be removed and sent to the laboratory in a procedure called a neck dissection. This is more often done when the tumor is intermediate or high grade, when it is large, or when imaging or examination has suggested that lymph nodes may be involved.

Negative lymph node — No tumor cells are found in the node.
Positive lymph node — Tumor cells are found inside the node. The report will describe how many nodes contain tumor, the size of the largest deposit, and whether the tumor has grown beyond the outer wall of the node — a feature called extranodal extension.

Spread to lymph nodes is uncommon in low-grade mucoepidermoid carcinoma but is much more frequent in high-grade tumors.

Pathologic stage (pTNM)

Pathologic staging describes the size of the tumor and how far it has spread, based on the findings at surgery. It uses the TNM system: T stands for the size and extent of the primary tumor, N stands for involvement of nearby lymph nodes, and M stands for spread to distant parts of the body. Staging applies only to mucoepidermoid carcinomas of the major salivary glands. Tumors of the minor salivary glands are staged using the system for the area where they started (such as the oral cavity or oropharynx).

Tumor stage (pT)

T1 — The tumor is 2 cm or smaller and confined to the salivary gland.
T2 — The tumor is larger than 2 cm but not larger than 4 cm and is still confined to the salivary gland.
T3 — The tumor is larger than 4 cm, or has spread beyond the salivary gland into surrounding soft tissue (extraparenchymal extension).
T4a — The tumor has invaded skin, the jawbone, the ear canal, or the facial nerve.
T4b — The tumor has invaded the base of the skull, nearby bones, or major blood vessels.

Nodal stage (pN)

N0 — No tumor cells in any examined lymph nodes.
N1 — A single lymph node on the same side of the neck contains tumor, and is 3 cm or smaller, with no extranodal extension.
N2a — A single lymph node on the same side of the neck is between 3 and 6 cm, or any lymph node shows extranodal extension.
N2b — Multiple lymph nodes on the same side of the neck contain tumor, none larger than 6 cm, with no extranodal extension.
N2c — Lymph nodes on both sides of the neck or on the opposite side from the tumor contain tumor, none larger than 6 cm, with no extranodal extension.
N3a — A lymph node larger than 6 cm contains tumor.
N3b — Any positive lymph node shows extranodal extension (apart from the single small node category covered under N2a).

What is the prognosis?

The outlook for mucoepidermoid carcinoma depends mostly on the grade of the tumor:

Low grade — Excellent outlook. The 5-year survival rate is greater than 95%. Surgery alone is curative for most patients, and recurrence is uncommon.
Intermediate grade — Good outlook. The 5-year survival rate is approximately 70–90%. Most patients are treated with surgery, often followed by radiation therapy.
High grade — More guarded outlook. The 5-year survival rate is approximately 30–50%. These tumors are more likely to come back near the original site or spread to lymph nodes and to distant sites such as the lungs.

Several other features in the pathology report can also affect the outlook:

Tumor size larger than 4 cm — Larger tumors are more likely to have spread and to come back.
Extraparenchymal extension — Tumors that have grown beyond the salivary gland are at higher risk of coming back.
Positive surgical margins — Incompletely removed tumors are more likely to come back.
Lymph node involvement — Spread to lymph nodes raises the risk of distant spread and worsens overall prognosis.
Perineural and lymphovascular invasion — Both are linked with a higher risk of the tumor coming back.
MAML2 fusion status — Tumors that have a MAML2 fusion tend to behave more favorably than tumors without the fusion. Most low- and intermediate-grade tumors have the fusion. Most high-grade tumors do not.

What happens after the diagnosis?

Treatment for mucoepidermoid carcinoma is led by a head and neck surgeon. The surgeon often works with a radiation oncologist, a medical oncologist (when high-grade or advanced disease is present), and a speech-language pathologist for any rehabilitation needs. Treatment is guided mainly by the grade of the tumor.

Surgery — The main treatment for all grades. For parotid tumors, this is usually a parotidectomy. The facial nerve is preserved whenever possible. Submandibular tumors are removed along with the entire affected gland. Tumors of the palate or other minor salivary sites are removed along with a rim of healthy tissue.
Neck dissection — Removal of lymph nodes from one or both sides of the neck. Often done for intermediate- and high-grade tumors, large tumors, and any tumor with clinical or imaging evidence of lymph node involvement. Neck dissection is usually not needed for small, low-grade tumors.
Radiation therapy after surgery — Recommended for intermediate- and high-grade tumors, when surgical margins are positive or close, when perineural or lymphovascular invasion is identified, when lymph nodes are involved, or for advanced-stage tumors. Low-grade tumors removed with negative margins usually do not need radiation. Radiation is given as a series of daily treatments over several weeks.
Chemotherapy — Reserved for selected patients with high-grade or advanced disease, often in combination with radiation. Chemotherapy alone is generally not very effective in mucoepidermoid carcinoma.
Targeted therapy and clinical trials — Several drugs that target the molecular pathways activated by the MAML2 fusion are being studied in clinical trials. Patients with advanced or recurrent disease should ask whether a clinical trial is available.
Long-term surveillance — Regular clinical examination of the head and neck, with imaging as needed, continues for many years after treatment.

Questions to ask your doctor

Where exactly did the tumor start, and how large was it?
What grade is my tumor — low, intermediate, or high?
What is the pathologic stage (pT, pN, and overall TNM stage) of my cancer?
Was the tumor completely removed? What were the surgical margins?
If a margin was positive or close, will I need more surgery or radiation therapy?
Were perineural or lymphovascular invasion identified?
Were any lymph nodes involved by tumor, and was extranodal extension present?
Was molecular testing performed, and was a MAML2 fusion identified?
Will I need radiation therapy or chemotherapy after surgery?
What is my estimated risk of the cancer coming back?
What is the schedule for follow-up examinations and imaging, and how long will it continue?
Will I have any lasting facial weakness, numbness, or dry mouth from the surgery?
If I had radiation therapy in the past, are my children or other family members at any added risk?
Are there any clinical trials I should consider?