Epithelial-Myoepithelial Carcinoma: Understanding Your Pathology Report

by Jason Wasserman MD PhD FRCPC
May 6, 2026

Epithelial-myoepithelial carcinoma (EMC) is a type of cancer that starts in the salivary glands — the glands that make saliva. It is uncommon overall, accounting for fewer than 1% of all salivary gland cancers. The name reflects the two cell types that make up the tumor: inner ductal cells (also called epithelial or luminal cells) and outer myoepithelial cells. Because the tumor contains these two cell populations, it is also called a biphasic salivary gland neoplasm (“bi” means two). Most epithelial-myoepithelial carcinomas grow slowly, are limited to the gland in which they started, and are cured by surgery alone.

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 epithelial-myoepithelial carcinoma?

The cause of epithelial-myoepithelial carcinoma is not known in most cases. It is not strongly linked to smoking, alcohol, or any other lifestyle factor, and it is not part of any known inherited cancer syndrome. We do know, however, that about half of epithelial-myoepithelial carcinomas have a specific change in their DNA — a mutation in the HRAS gene. The mutation locks the HRAS protein in the “on” state, sending a constant signal that tells tumor cells to grow and divide. A smaller number of tumors have a mutation in a related gene called AKT1. These genetic changes happen by chance during a person’s lifetime. They are not inherited and cannot be passed to children.

A small number of epithelial-myoepithelial carcinomas arise within a long-standing benign salivary gland tumor called a pleomorphic adenoma. When this happens, the diagnosis is called carcinoma ex pleomorphic adenoma (“ex” means “from”). This is why a pleomorphic adenoma that has been stable for years and then suddenly starts to grow is taken seriously and is usually removed promptly.

Where does epithelial-myoepithelial carcinoma start?

Epithelial-myoepithelial carcinoma can start in any salivary gland, but is most often found in the parotid gland — the largest salivary gland, which sits in front of and below each ear. About 60–75% of cases arise in the parotid gland. The remainder occur in the submandibular gland (under the jaw), the sublingual gland (under the tongue), or in the small minor salivary glands distributed throughout the lining of the mouth and throat. Rarely, tumors with the same appearance arise in the large airways of the lungs.

Epithelial-myoepithelial carcinoma can occur at any age but is most common between 60 and 80 years old. It is slightly more common in women than in men.

What are the symptoms of epithelial-myoepithelial carcinoma?

Most epithelial-myoepithelial carcinomas grow slowly and produce only mild symptoms in the early stages:

Painless lump or swelling — A slow-growing, painless mass in the salivary gland is the most common finding by far. 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.
Pain or tenderness — Uncommon at first. New pain may be a warning sign that the tumor has invaded a nerve or has undergone high-grade transformation.
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 uncommon in epithelial-myoepithelial carcinoma and, when present, suggests a more aggressive tumor.
Sudden change in a long-standing lump — A pleomorphic adenoma that has been stable for years and then suddenly begins to grow more rapidly is a warning sign of carcinoma ex pleomorphic adenoma.

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 two distinct cell populations arranged in layers — the defining feature of this cancer:

Ductal (luminal) cells — The inner layer of cells that lines small tube-like spaces. These cells are pink-staining (eosinophilic) and have a uniform appearance.
Myoepithelial (abluminal) cells — The outer layer of cells that surrounds the ductal cells. These cells often appear clear or pale because their cytoplasm (the fluid inside the cell) is filled with sugar (glycogen).

The double-layered tubular pattern is the hallmark of epithelial-myoepithelial carcinoma. The thickness of the myoepithelial layer can vary — from a single cell thick to many cells thick — and in some areas the myoepithelial cells can dominate, giving a more solid appearance. Other patterns the pathologist may describe include cribriform (sieve-like), basaloid (small densely packed cells), papillary (finger-like projections), and double-clear cell layers. In some cases the cells take on features of sebaceous (oil-producing) cells or squamous cells. The cells themselves usually show only mild to moderate variation in size and shape, which is why most epithelial-myoepithelial carcinomas are considered low grade.

To confirm the diagnosis, the pathologist often uses immunohistochemistry, a stain that highlights specific proteins in the tumor cells. The two cell populations stain for different proteins, which is the key to confirming the diagnosis. The ductal cells are typically positive for cytokeratins (such as CK7), while the myoepithelial cells are typically positive for S100, SOX10, p63, p40, smooth muscle actin, and calponin. Demonstrating both cell populations is essential — a tumor with only one of the two cell types is not epithelial-myoepithelial carcinoma. In cases where the diagnosis is uncertain, molecular testing for an HRAS mutation can be helpful, since this mutation is found in about half of epithelial-myoepithelial carcinomas and is uncommon in the other tumors that can mimic it. The most useful tests for finding this mutation are next-generation sequencing (NGS) and a related test that looks for the specific hotspot change in the HRAS gene. Once the diagnosis is confirmed, additional imaging is used to assess spread before treatment is planned.

High-grade transformation

High-grade transformation means that part of the tumor has changed into a much more aggressive form of cancer. In areas of high-grade transformation, the tumor cells lose the typical biphasic pattern of epithelial-myoepithelial carcinoma. They become very abnormal looking (atypical and pleomorphic), divide rapidly (with many mitotic figures), and often show areas of necrosis (cell death). High-grade transformation is uncommon in epithelial-myoepithelial carcinoma, but when present, the tumor is much more likely to spread to lymph nodes and to distant sites such as the lungs. Treatment is usually stronger when this finding is reported, often including a neck dissection (removal of lymph nodes from the neck) and radiation therapy after surgery.

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 classic epithelial-myoepithelial carcinoma and much more common when high-grade transformation is present. 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 epithelial-myoepithelial 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.
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 epithelial-myoepithelial carcinoma are those in the neck. Spread to lymph nodes is uncommon in classic epithelial-myoepithelial carcinoma but is more frequent when high-grade transformation is present. 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 shows worrying features — such as high-grade transformation or large size — rather than as a routine part of treatment.

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.

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 epithelial-myoepithelial 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 most patients with epithelial-myoepithelial carcinoma is good. The tumor is generally slow-growing, and complete surgical removal cures most patients. The 5-year overall survival rate for classic epithelial-myoepithelial carcinoma is greater than 80%, and the 10-year survival rate is approximately 70–75%. The main long-term concern is local recurrence — the tumor coming back in the same area after surgery — which has been reported in 30–40% of patients, sometimes years later. Spread to distant sites, such as the lungs, is uncommon (around 7–25% lifetime), and spread to lymph nodes is unusual unless high-grade transformation is present.

Several features in the pathology report can identify patients at higher risk of a worse outcome:

High-grade transformation — The single most important warning sign. Survival drops substantially when this is present.
Tumor size larger than 4 cm — Larger tumors are more likely to come back or to spread.
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.
Perineural and lymphovascular invasion — Both are linked with a higher risk of the tumor coming back.
Lymph node involvement — Spread to lymph nodes raises the risk of distant spread.

What happens after the diagnosis?

Treatment for epithelial-myoepithelial carcinoma is led by a head and neck surgeon. The surgeon often works with a radiation oncologist and a medical oncologist (when high-grade or advanced disease is present). The main treatment is surgery to remove the entire tumor.

Parotidectomy — Removal of part or all of the parotid gland. Most epithelial-myoepithelial carcinomas of the parotid gland are treated with a superficial parotidectomy or, for deeper tumors, a total parotidectomy. The facial nerve is preserved whenever possible. Submandibular and sublingual tumors are removed along with the entire affected gland.
Neck dissection — Removal of lymph nodes from one or both sides of the neck. Done when there is clinical or imaging evidence of lymph node involvement, when high-grade transformation is present, or when the tumor is very large. Neck dissection is often not needed for small, classic epithelial-myoepithelial carcinomas.
Radiation therapy after surgery — Recommended when high-grade transformation is present, when surgical margins are positive or close, when perineural or lymphovascular invasion is identified, when lymph nodes are involved, or for advanced-stage tumors. Radiation is given as a series of daily treatments over several weeks.
Standard chemotherapy — Generally not very effective in epithelial-myoepithelial carcinoma and is reserved for selected patients with advanced disease.
Clinical trials — Drugs that target the HRAS mutation found in many epithelial-myoepithelial carcinomas (such as tipifarnib) are being studied in clinical trials for various HRAS-mutated cancers. 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 because of the risk of late local recurrence.

Questions to ask your doctor

Where exactly did the tumor start, and how large was it?
Did the tumor develop on its own, or did it arise within a previous pleomorphic adenoma?
What is the pathologic stage (pT, pN, and overall TNM stage) of my cancer?
Was high-grade transformation seen anywhere in the tumor?
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 an HRAS or AKT1 mutation found?
Will I need radiation therapy 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 dryness of the mouth from the surgery?
Are there any clinical trials I should consider, particularly for HRAS-targeted drugs?