Conditions: Submandibular Gland Tumors

Where the submandibular gland is, and why it matters

You have two submandibular glands, each about the size of a walnut, sitting just beneath the lower jaw on either side of the upper neck. They are two of the major salivary glands and produce much of the saliva that keeps the mouth moist, especially between meals. Each gland drains its saliva through a narrow tube (Wharton's duct) that opens on the floor of the mouth, under the tongue.

Three important nerves run very close to the gland, which is why any growth here is taken seriously and why surgery in this area is done carefully. These are the nerve branch that moves the lower lip (the marginal mandibular nerve), the nerve that gives sensation and taste to the tongue (the lingual nerve), and the nerve that moves the tongue (the hypoglossal nerve). The gland also sits within the "level I" region of the neck, an area rich in lymph nodes that drain the mouth, lips, and face.

Three things that make the submandibular gland different from the parotid

If you have read the parotid handouts, a few important contrasts are worth knowing up front.

• A lump here is more likely to be cancer. As a general rule, the smaller the salivary gland, the higher the chance that a tumor in it is malignant. In the parotid, only about 1 in 5 tumors is cancerous; in the submandibular gland, roughly 4 to 5 out of 10 tumors are malignant — about double the rate. This does not mean most under-the-jaw lumps are cancer (far from it, as explained below), but it does mean a true tumor of this gland deserves prompt, careful evaluation.
• Most swellings here are not tumors at all — they are stones or infection. In one large surgical series, nearly half of removed glands contained a stone, a third had inflammation, and only about one in five actually harbored a tumor. Salivary stones are the single most common cause of a swollen submandibular gland.
• This gland does not contain lymph nodes inside it. Unlike the parotid, which has lymph nodes trapped within its substance, the submandibular gland has lymph nodes only around it, not inside. This is why cancers rarely "seed" into the gland itself through the lymphatic system, and why true spread into the gland is uncommon.

Benign (non-cancerous) tumors

Most benign submandibular tumors cause a slow-growing, painless, firm, rubbery lump under the jaw that can often be moved slightly under the skin.

Pleomorphic adenoma (also called a benign mixed tumor) is by far the most common benign tumor here, making up the large majority — in many series over 90% — of non-cancerous growths in this gland. It grows slowly over months to years and is typically painless. It is benign, but two features make removal the usual recommendation: it tends to come back if not fully removed, and over many years a small percentage (roughly 5–15%) can transform into a cancer. (How it is managed is in the treatment handout.)

Other benign tumors are much rarer in this gland. Oncocytoma is the second most common but still uncommon. Warthin tumor, which is very common in the parotid and strongly linked to smoking, is distinctly rare in the submandibular gland. Myoepithelioma and basal cell adenoma are occasionally seen.

Cancerous (malignant) tumors arising in the gland

Submandibular cancers also often start as a painless lump, which is part of why they can be mistaken at first for a harmless swelling or a stone. Warning features that raise concern for cancer include pain, a mass that feels fixed to the skin or deeper tissues, weakness of the lower lip, numbness or altered sensation of the tongue, and firm lumps (enlarged lymph nodes) in the neck. Because these signs are not always present early, nearly half of submandibular cancers are found at a more advanced stage. Clinical examination alone cannot reliably tell a benign lump from a cancerous one, which is why testing (below) is important.

Adenoid cystic carcinoma is the most common cancer of the submandibular gland — a notable difference from the parotid, where a different cancer predominates. It grows slowly but persistently, has a strong tendency to creep along nerves (which can cause pain, numbness, or weakness), and can reappear or spread to distant sites such as the lungs even many years after treatment. Mucoepidermoid carcinoma is the second most common; its behavior ranges from indolent to aggressive depending on its grade. Adenocarcinoma, carcinoma arising within a pre-existing pleomorphic adenoma (a long-standing benign lump that suddenly starts changing or growing), and salivary duct carcinoma (an aggressive, high-grade cancer) are also seen. Acinic cell carcinoma and primary squamous cell carcinoma of the gland are less common here than elsewhere. As a group, submandibular cancers tend to carry a somewhat less favorable outlook than parotid cancers because they more often spread to lymph nodes or distant organs.

Cancer that spreads to the gland from somewhere else (metastatic tumors)

Because the submandibular gland has no lymph nodes inside it, cancer spreading into the gland itself is rare. When it does happen, it occurs in one of two main ways: a nearby cancer (such as a floor-of-mouth cancer) grows directly into the gland, or a cancer elsewhere in the body travels to it through the bloodstream. In a large review of oral cancers, the submandibular gland itself was involved in only about 2% of cases, nearly always by direct invasion rather than isolated spread.

When cancer does reach the gland, the usual sources are skin cancers of the face and lip — cutaneous squamous cell carcinoma and melanoma — although these far more often go to the parotid than to the submandibular gland. Among cancers from below the collarbones, the lung, kidney (sometimes appearing years after the original tumor was treated), and breast are the most frequently reported sources. It is worth distinguishing two things that sound alike: cancer inside the gland is rare, but cancer in the lymph nodes next to the gland (level I nodes) is common, since those nodes are a frequent landing spot for mouth, lip, and facial cancers.

Lymphoma

Lymphoma is a cancer of the immune system's lymphocytes, and it can involve the salivary glands. Only about 9% of salivary gland lymphomas occur in the submandibular gland (most occur in the parotid). When lymphoma does arise here, the most common types are diffuse large B-cell lymphoma, follicular lymphoma, and MALT (marginal zone) lymphoma, in roughly similar proportions. MALT lymphoma is typically slow-growing (indolent) and tends to stay localized, with an excellent long-term outlook.

An important link is with Sjögren syndrome, an autoimmune condition that attacks the salivary and tear glands (described below). People with Sjögren syndrome have a substantially increased risk of developing lymphoma — most often MALT lymphoma — compared with the general population. Signs that raise concern in someone with Sjögren syndrome include persistent gland enlargement, swollen lymph nodes, and an enlarged spleen. A gland swelling that is hard, fixed, persistent, and one-sided — particularly in someone with a known autoimmune condition — warrants evaluation to rule out lymphoma.

Conditions that can look like a tumor but are not

Most swellings under the jaw are not tumors. Several non-cancerous conditions can produce a lump or swelling that closely mimics a tumor, and telling them apart often requires imaging and sometimes a tissue sample.

Salivary stones (sialolithiasis) are the most common cause of submandibular swelling and the single most important mimic. Remarkably, 80–90% of all salivary stones form in the submandibular gland, because of its uphill drainage against gravity, its long winding duct, and its thicker, more mineral-rich saliva. The classic clue is swelling and pain that come on around meals, when saliva is stimulated but cannot get past the blockage, then ease afterward. Sometimes a stone can be felt as a hard lump in the floor of the mouth.

Sialadenitis is inflammation or infection of the gland, often triggered by a stone blocking the duct. It can be sudden (with a painful, swollen gland and sometimes pus from the duct opening) or chronic and recurring. Pain and a pattern of flare-and-settle, especially around eating, help distinguish inflammation from a tumor.

Chronic sclerosing sialadenitis (Küttner tumor) deserves special mention because its name is misleading: it is not a true tumor. It is a chronic scarring inflammation that almost exclusively affects the submandibular gland and produces a firm, hard swelling that feels exactly like a cancer on examination — which is why it was historically called a "tumor." It is now recognized as often being part of IgG4-related disease (below), and it is frequently associated with stones. Because it so convincingly mimics cancer, the diagnosis is often confirmed only after the gland is examined under the microscope.

IgG4-related disease is a systemic immune condition that causes painless, firm swelling of glands and other organs, with a particular tendency to enlarge both submandibular glands. It can also affect the tear glands, parotid glands, pancreas, kidneys, and other sites. A blood test (IgG4 level) is often but not always elevated, and the diagnosis requires excluding mimics such as lymphoma.

Sjögren syndrome is an autoimmune disease that causes dry eyes and dry mouth from immune attack on the glands. It tends to affect the parotid glands more than the submandibular, but it can cause gland enlargement that mimics a tumor, and (as noted above) it carries a long-term lymphoma risk.

Sialadenosis (sialosis) is a soft, usually symmetrical, non-painful swelling of the salivary glands linked to conditions such as diabetes, heavy alcohol use, eating disorders, thyroid disease, and malnutrition. It more often affects the parotid glands but can involve the submandibular glands.

Plunging ranula is a mucus-filled cyst that originates from the sublingual gland and dips down into the neck through a gap in the floor-of-mouth muscle, producing a soft swelling under the jaw that can be mistaken for a submandibular gland mass. It is typically soft and fluctuant.

Enlarged lymph nodes (lymphadenopathy) in this region are a very common mimic, since the level I nodes swell in response to dental infections, mouth and throat infections, and a range of other causes. A helpful clinical clue: a lump that can be rolled over the lower edge of the jawbone is more likely a lymph node, whereas one felt from both inside the mouth and the neck at once is more likely the gland itself.

How these conditions are evaluated

Because examination alone cannot reliably separate harmless swellings, stones, and inflammation from true tumors, a combination of tests is usually used.

• Ultrasound is typically the first imaging test. It is quick, uses no radiation, can distinguish the gland from nearby structures, can spot stones, and can guide a needle to sample a lump.
• CT or MRI scans are added when a tumor is suspected or more detail is needed. MRI is especially good at showing a tumor's extent, its relationship to nerves, and whether it is tracking along a nerve.
• Fine-needle aspiration (FNA) uses a thin needle to draw cells for analysis and is the standard way to sample a salivary gland lump; in some centers a slightly larger core-needle biopsy is used for greater accuracy. An open surgical biopsy is generally avoided for these masses.
• Blood tests may be ordered when an autoimmune or IgG4-related condition is suspected (for example, to look for Sjögren-related antibodies or an elevated IgG4 level).

No single test is perfect, and the pieces are interpreted together. In some cases the exact diagnosis is confirmed only after the gland is removed and examined under the microscope.

When to seek medical attention

Have a lump or swelling under the jaw evaluated, particularly if it:

• Lasts more than two to three weeks or keeps growing
• Is hard, feels fixed, or is tender
• Swells and hurts around meals (suggests a stone)
• Is accompanied by weakness of the lower lip, or numbness or altered sensation of the tongue
• Comes with firm lumps in the neck, unexplained weight loss, drenching night sweats, or persistent fevers

Most swellings in this area turn out to be stones, infection, or another benign condition — but because a true tumor here is more likely to be cancerous than at other salivary sites, a persistent or unexplained lump should always be checked.

Questions you may wish to ask your care team

• Is my swelling likely a stone, an infection, an autoimmune condition, or a true tumor?
• Do I need an ultrasound, CT, or MRI, and will I need a needle biopsy?
• If this is a tumor, is there any indication it could be cancerous?
• Are any of the nearby nerves (lip, tongue) involved?
• Should any blood tests be done to check for an autoimmune or IgG4-related cause?