Multiple endocrine neoplasia (MEN): Tumors of the endocrine system

This page was reviewed under our medical and editorial policy by

Maurie Markman, MD, President, Medicine & Science

This page was updated on February 28, 2022.

Multiple endocrine neoplasia (MEN) syndromes are rare genetic disorders of the endocrine system, which is the body’s grouping of hormone-producing glands. The glands in the network produce hormones—also known as the chemical substances that travel through the bloodstream to help cells and tissues do their job, including growth, digestion and sexual function.

This condition is also known as:

  • Adenomatosis, familial endocrine
  • Familial endocrine adenomatosis
  • Endocrine neoplasia, multiple
  • Multiple endocrine adenomatosis (MEA)
  • Multiple endocrine neoplasms

People with MEN syndromes are likely to develop tumors—either benign (noncancerous) or malignant (cancerous)—on the endocrine glands, as well as other organs and tissues.

There are different forms of multiple endocrine neoplasia. The genes that are affected, the types of hormones involved, and the signs and symptoms of the disease determine the type.

Among the most common are type 1 (MEN1) and type 2 (MEN2).

Type 2 has subtypes:

How common is MEN?

About one in 30,000 people are affected by multiple endocrine neoplasia type 1, according to the U.S. National Library of Medicine. Type 2 is even less common, with about one case in 35,000 people.

  • Of type 2, type 2A is the most common.
  • Type 2B is the least common (constituting only about 5 percent of type 2 cases).
  • FMTC accounts for 10 percent to 20 percent of MEN2 cases, according to GeneReviews.

What causes type 1 and type 2?

A mutation in the MEN1 gene—which provides the blueprint for making the protein menin, a tumor suppressor—is the cause of type 1.

Typically, every cell has two copies of each gene (one from each parent). MEN1 is autosomal dominant, meaning it only takes one parent with a gene mutation to pass it along.

That means offspring have a 50 percent chance of inheriting the mutated gene, according to the American Society of Clinical Oncology (ASCO). About 10 percent of those with a faulty MEN1 gene have no family history of the disease (they have what’s known as a de novo, or new mutation).

Type 2 is caused by a mutation in the RET gene. It, too, is involved in telling cells how to make protein—and the protein it provides instructions for is necessary for the normal development of the kidney and nerve cells, as well as for sperm production.

Like type 1, type 2 only requires one parent with a gene mutation. According to the ASCO, if either parent has the mutation, the child has a 50 percent chance of inheriting it. Type 2 also may be a de novo (new) mutation. The majority of people with MEN2B don’t have an inherited mutation. Meanwhile, fewer than 5 percent of people with MEN2A are thought to have a new mutation.

Risk factors for MEN

People with this condition develop tumors that produce extra hormones.


MEN1 typically involves tumors of the:

  • Parathyroid glands, behind the thyroid glands in the neck (According to the Genetic and Rare Diseases Information Center (GARD), most [90 percent] of those with MEN1 develop parathyroid tumors by age 20 to 25.)
  • Pituitary gland, found in the brain
  • Pancreas, found in the abdomen near the stomach and intestines
  • Adrenal glands, located above the kidneys
  • Lining of the lungs or digestive tract, known as carcinoid tumors

Most tumors in people with MEN1 are noncancerous. However, according to ASCO, one out of three pancreatic neuroendocrine and mediastinal neuroendocrine tumors are malignant. Special tumors of the gastrointestinal tract and carcinoid tumors are most likely to become malignant as well.

People with MEN1 also may have tumors not related to the endocrine system, including:

  • Facial angiofibroma, made of blood vessels and fibrous tissue
  • Collagenoma, a flesh-colored mass on the skin
  • Lipoma, made of fatty tissue
  • Leiomyoma, a smooth muscle mass
  • Meningioma and ependymoma, uncommon tumors formed from the nervous system

These tumors may develop at any age. Complications vary depending on the location and size of tumors.


MEN2 typically involves tumors of the:

  • Thyroid gland, known as medullary thyroid cancer (MTC): These may spread to the lymph nodes and advance to other areas of the body, such as the lungs, liver and bones. Most people with MEN2 (80 percent to 99 percent) develop this cancer. MTC is more common in women than men. The National Cancer Institute characterizes this as one of the rarest types of thyroid cancer—with 3 percent to 4 percent of thyroid cancer patients having MTC.
  • Adrenal glands, known as pheochromocytoma (PHEO), which are located above the kidneys: PHEO is usually benign and unlikely to spread.
  • Parathyroid glands, which produce a parathyroid hormone (PTH) that regulates blood calcium levels: These tumors are typically benign but may lead to high calcium levels.

MEN type 1 symptoms

Symptoms vary depending on which endocrine and nonendocrine glands are involved.

Adrenal tumors may cause:

  • Abdominal pain
  • Diabetes
  • Excessive hair growth
  • Headaches
  • High blood pressure
  • Irregular heartbeat
  • Panic attacks
  • Stretch marks
  • Weakness

Carcinoid tumors may cause:

  • Diarrhea
  • Flushing of the face and upper chest
  • Trouble breathing

Parathyroid tumors may cause:

  • Constipation
  • Dehydration
  • Depression
  • Fatigue
  • Fragile bones
  • Hypertension
  • Kidney stones
  • Nausea and vomiting
  • Weight loss

Pituitary tumors may cause:

  • Decreased fertility in men
  • Diminished sexual desire in men
  • Erectile dysfunction
  • Headaches
  • Irregular or no menstrual cycle in women
  • Nausea and vomiting
  • Vision problems

It’s important to note that not everyone develops every symptom.

MEN type 2 symptoms

As with most diseases, symptoms vary from person to person.

Medullary thyroid carcinoma symptoms include:

  • Throat lump
  • Hoarse voice
  • Difficulty breathing

If the tumor remains small, the patient may not have symptoms.

PHEO symptoms include:

  • Abdominal pain
  • Anxiety
  • Constipation
  • Chest pain
  • Dizziness
  • Elevated blood sugar
  • Facial redness (flushed skin)
  • Heart palpitations
  • Increased blood pressure
  • Increased respiratory rate
  • Irritability
  • Nausea
  • Nervousness
  • Pale skin
  • Perspiration
  • Severe headaches
  • Vision problems
  • Weight loss

Parathyroid tumor symptoms include:

  • Abdominal pain
  • Bone pain
  • Confusion
  • Depression
  • Fatigue
  • Gastroduodenal ulcers (in stomach and small intestine)
  • Insomnia
  • Kidney issues, including upper back pain and frequent urination
  • Malaise
  • Neck lump
  • Weakness
  • Vomiting

Diagnosing MEN

The earlier the diagnosis, the better. This allows the patient to be monitored for tumors and other symptoms before they become more serious.

Patients are likely to undergo genetic testing, which may be performed with a blood or saliva sample.

In up to one in four cases, genetic testing may not find a mutation—even though the patient is exhibiting symptoms of MEN, according to the National Institute of Diabetes and Digestive and Kidney Diseases. The patient may have MEN and an unknown mutation, or a mutation in a different gene. Doctors may look for other causes of the symptoms in this case.

MEN type 1 diagnosis

Diagnosis depends on the presence of several symptoms. Patients are likely to be diagnosed with MEN1 if they have one of the following:

  • Two or more tumors found in the parathyroid glands, pituitary gland, pancreas or other parts of the digestive tract
  • A single tumor in these glands or organs and a first-degree relative diagnosed with MEN1
  • A genetic test that shows a MEN1 mutation, even if there are no signs or symptoms

MEN type 2 diagnosis

Doctors may diagnose MEN2 after finding:

  • Two or more specific endocrine tumors, such as MTC, PHEO or parathyroid tumor
  • Distinctive facial features
  • Other family members who’ve been diagnosed with this disorder

For both type 1 and type 2, the patient is likely to need:

Some tumors also may need to be biopsied to determine whether they are benign or malignant.

Treatment for MEN

Treatment requires a team of specialists working together to care for the patient’s needs. Members of this care team are likely to include:

MEN type 1 treatment

There’s no cure for MEN1, but it’s possible to live a long and productive life with this disease. Doctors may need to monitor the patient’s tumors and provide treatment on an as-needed basis.

To monitor the disease, the patient may need regular screening tests, including:

  • Blood tests to look for elevated hormone levels and tumor markers
  • Imaging tests to monitor the size and growth of known tumors and to look for new tumors

Surgery also may be needed to remove tumors, or the patient may be given medication to suppress tumor growth or other problems.

  • Parathyroid tumors are likely to be removed, or may be treated with medication if they aren’t operable.
  • Pancreas and digestive tract tumors may be treated with medications to control symptoms. They may be removed surgically or frozen or burned and left in place. In rare cases, the patient may receive intravenous drugs to kill the cancer cells.
  • Pituitary gland tumors may be treated with medication, surgery or radiation therapy.

MEN type 2 treatment

Treatment depends on a number of factors, including:

  • Whether cancer has developed and if and how far it’s spread
  • The severity of symptoms caused by excess hormone production

The thyroid may be removed during a procedure known as a thyroidectomy. This is often a preventive step. Once it’s removed, the patient may need to take thyroid replacement supplements.

MEN2 PHPT (parathyroid tumors) may be treated with medication. Some people undergo surgery to remove the parathyroid gland. Some healthy tissue from the parathyroid gland may be replanted in the forearm, so the patient doesn’t develop post-op hypoparathyroidism, which requires treatment with calcium and vitamin D for the duration of life.

PHEO is also treated with removal of one or both of the adrenal glands. The patient may need chemotherapy and radiation as follow-up for any tumors that have spread or are malignant.

Genetic counseling

Genetic counseling also may be part of the treatment plan, helping patients and their families learn:

  • The hows and whys
  • How to manage the disease
  • How to make the best decisions for the whole family

Genetic counseling also may help the patient weigh decisions that have to be made when given the results.

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