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This page was reviewed under our medical and editorial policy by
Maurie Markman, MD, President, Medicine & Science at CTCA.

This page was updated on June 14, 2022.

Thymoma

Thymoma is a type of tumor that occurs in the thymus gland, a small organ in the upper chest that makes up part of the lymphatic system. The thymus produces white blood cells, which are used by the body to fight off infection.

Thymoma is one of two types of thymic epithelial tumors, the other being thymic carcinoma. Both are rare cancers, although each behaves differently. Thymomas are more slow-growing, while thymic carcinomas tend to grow faster and spread.

Thymomas are diagnosed in about 400 people every year, according to the American Society of Clinical Oncology.

Thymoma symptoms

Sometimes, thymomas may not show symptoms. However, the most common symptoms include:

  • Shortness of breath
  • Persistent cough
  • Pain in the chest
  • Double vision
  • Swelling in the face or arm
  • Eyelids that droop Fatigue
  • Dizziness

Anyone experiencing such symptoms should see a doctor. Even though the symptoms may be caused by different conditions, it’s best to have a physical examination to rule out any health issues.

Causes and risk factors

There are no known causes or risk factors for thymomas. But there seems to be a relationship between thymic cancers and a few autoimmune paraneoplastic disorders, particularly myasthenia gravis (MG). About 30 to 65 percent of patients with thymomas have MG as well, though not all people with MG have thymomas, according to the American Cancer Society.

Thymoma is linked to other autoimmune diseases as well, including good syndrome (GS) and pure red cell aplasia (PRCA).

In the United States, thymic cancers tend to be more common in people of Asian and Pacific Islander heritage. They’re also more likely to develop with advancing age.

How is thymoma diagnosed?

If thymoma is suspected, doctors may conduct a physical examination and review the patient’s medical history, taking into account symptoms, age and pre-existing health conditions.

There are also a number of diagnostic tools that allow doctors to look for thymoma within internal areas of the body. These include:

If the scans reveal abnormal results, a biopsy may be performed, which allows the doctor to definitively diagnose a tumor as cancerous. A biopsy may be done with a needle or surgically. The surgical biopsy, known as a Chamberlain procedure, involves making a cut near the breastbone and removing part of the tumor for a pathologist to examine.

If it’s clear from the imaging tests that a thymoma is present, doctors may skip the biopsy process and go straight to removing the tumor.

During a diagnosis, the doctor may share the stage of cancer, which describes the disease’s growth and spread. This detail is necessary, as it guides treatment options. Thymic tumors are also assigned a classification type, based on the pattern of cells within the tumor.

A diagnosis of thymoma may be unexpected and frightening, so patients should ask their care team plenty of questions to better understand the disease and next steps.

What do the thymoma stages mean?

Thymoma and thymic cancer follow the same staging, from stage 1 to stage 4:

  • Stage 1 thymoma is inside the capsule that surrounds the thymus gland. The cancer hasn’t spread to other parts of the body.
  • Stage 2 thymoma has spread from the thymus gland into the surrounding fat or the chest cavity lining.
  • Stage 3 thymoma has spread to the lung, the sac around the heart or the large blood vessels that carry blood to the heart.
  • Stage 4 thymoma has two stages. Stage 4A thymoma has spread around the lungs or heart, and stage 4B thymoma has spread to the blood or lymph system.

Thymoma treatment

Doctors may recommend the most appropriate course of treatment based on the tumor’s stage, classification, and whether or not it’s spread to other parts of the body.

The most common thymoma treatment is surgery. Usually, this is a procedure called a median sternotomy, in which the breastbone is opened and the thymoma and surrounding tissue are removed. For smaller thymomas, the surgery may be done laparoscopically.

Other commonly used treatments include:

  • Radiation: Using high-energy X-ray beams directed at the tumor, cancer cells are destroyed.
  • Chemotherapy: A drug, or combination of drugs, is taken to kill cancer cells. Chemotherapy is used as a standalone treatment or before surgery to help shrink the tumor.
  • Targeted therapy: Doctors tailor treatment based on the properties of the tumor, such as its genes or proteins.
  • Immunotherapy: These drugs include checkpoint inhibitors that target the PD-1 and PD-L1 receptors on cells that help regulate the immune system.

It’s important to remember that all thymoma treatments may potentially lead to side effects, which may be uncomfortable. Doctors may help answer any questions about what to expect after treatment and how to reduce discomfort and side effects.

In fact, doctors are always the best source of information when it comes to managing thymoma or other cancers.

Thymoma survival rates

Survival rates vary based on certain factors, including:

  • The size of the thymoma
  • If and where the cancer has spread within the body
  • Age
  • Overall health
  • How well the cancer responds to treatment

The survival rate for thymus cancer is based on the number of people still alive five years after diagnosis.

In stage 1, when the thymoma is localized (it hasn’t spread outside the thymus gland), the five-year relative survival rate is 95 percent, according to the American Cancer Society. The rate is 78 percent when the cancer spreads regionally to nearby areas, and it’s 38 percent when it travels to more distant parts of the body.

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