What Is Thymus Cancer?

Thymus cancers are rare types of cancer that start in the cells of the thymus. The thymus is a small organ in your upper chest that helps make lymphocytes, a type of white blood cell, to help fight infections. These cancers often occur along with autoimmune diseases such as myasthenia gravis.

Thymomas and thymic carcinomas are the two most common types of thymus cancer. Together, thymomas and thymic carcinomas make up between 0.2% and 1.5% of all cancers.

This article focuses on thymomas and thymic carcinomas. It gives information about types, possible symptoms, diagnosis, treatment, prognosis, and related issues. 

Types of Thymus Cancer

Thymomas and thymic carcinomas are both parts of a larger group of cancers called thymic epithelial tumors (TETs). In both thymomas and thymic carcinomas, cancer first starts in cells that line the surface of the thymus (epithelial cells). Thymomas are about 5 times as common as thymic carcinomas. 

Thymomas grow slowly, and they rarely spread beyond the thymus. In contrast, thymus carcinoma is more likely to spread, and it is usually more difficult to treat than a thymoma. 

Microscopic Categories

The World Health Organization (WHO) further divides thymomas and thymic carcinomas into subcategories based on how they look under the microscope. You might be told that your thymoma is type A, type AB, or type B1, B2, or B3. Thymic carcinoma is sometimes described as type C.

Subcategories with letters that come later in the alphabet tend to have worse outcomes than those that come earlier in the alphabet.

Staging

Cancers can also be divided based on something called stages. The cancer’s stage gives specific information about how much it has spread in the body. Thymus cancers are assigned the numerals from 1 to 4, with a lower number implying less cancer spread. 

A person’s cancer might also be categorized based on its size, whether or not it has spread to nearby lymph nodes, and whether it has spread to distant parts of the body.

Other Cancers That Begin in the Thymus

Thymic neuroendocrine tumors (NETs) are another type of cancer that starts in your thymus. This type begins in the cells that release certain hormones. They have a lot of similarities to neuroendocrine tumors that start in other parts of the body, like the lungs.

Some cancers also begin in the white blood cells that are found in the thymus. These can turn into lymphomas such as Hodgkin's disease. But they aren’t what most people mean when they talk about thymus cancer. 

Some people also have cancer in the thymus that has spread there from other parts of the body, such as from the lungs. Cancer that spreads to other areas of the body is called metastatic cancer. 

Thymus Cancer Symptoms

Most people don’t have symptoms when they are first diagnosed with thymus cancer, but about one-third of people do. Some potential symptoms are:

• Cough
• Shortness of breath
• Chest pain
• Hoarse voice
• Swelling of the face, neck, and arms

Symptoms From Related Autoimmune Disease

Some people with cancer of the thymus also have symptoms of autoimmune disease. This happens when the immune system is inappropriately activated against a part of the body. (These diseases are called autoimmune paraneoplastic diseases when they occur along with cancer.)

The most common autoimmune disease associated with cancer of the thymus is myasthenia gravis. Nearly 50% of people with thymoma eventually develop myasthenia gravis. 

Some people with cancer of the thymus also have other autoimmune diseases, such as:

• Acquired pure red cell aplasia
• Rheumatoid arthritis
• Lupus
• Autoimmune thyroid disease
• Pernicious anemia

Causes of Thymus Cancer

In general, cancer occurs when a person's cells mutate. These mutations are small changes to the genetic material, or DNA. 

Everyone experiences mutations over time, and most of them aren’t a problem. However, sometimes a cell gets multiple mutations that cause it to start acting abnormally. It may start to spread and divide in ways it shouldn’t. This is the beginning of cancer.

Unlike with some other types of cancer, science doesn't have a good understanding of what causes thymus cancer specifically or the risk factors involved. Increased age is the main risk factor, however. 

Some scientists speculate that thymoma may be at least partly triggered by certain viruses, such as Epstein-Barr virus (EBV). However, this isn't known for certain.

How Is Thymus Cancer Diagnosed?

Some people experience symptoms of thymus cancer and look to a medical professional to determine the cause. Other times, a problem is first noticed only when a person has a chest X-ray done for other reasons. If a person is diagnosed with myasthenia gravis, it's standard to check for a thymoma as well.

As for all medical diagnoses, it will start with your healthcare provider getting a complete medical history and performing a physical exam. This may give clues about a possible thymus cancer and rule out other potential causes.

Various imaging tests can also be very helpful. One or more of the following might be used:

• Chest X-ray
• Computed tomography (CT) scan to get a more detailed view than an X-ray provides
• Magnetic resonance imaging (MRI) also to get more detailed information than on an X-ray
• Positron-emission tomography (PET) scan to learn the extent of cancer spread

These imaging tests can provide a fair amount of information to determine thymus cancer. However, a definitive diagnosis often requires surgery. When a specialist looks at part of the thymus under the microscope, they can diagnose thymus cancer and its specific characteristics.

What’s the Treatment for Thymus Cancer?

If possible, medical professionals treat thymus cancer through surgery. This is especially effective if the cancer has not spread in the body.

In adults, the thymus is no longer active; therefore, adults with thymus cancer usually get their entire thymus removed (thymectomy). In a child, surgeons might try to remove only the cancerous part.

Nonsurgical Options

Depending on the circumstances, your treatment team may recommend one or more other therapies, either in addition to surgery or instead of it. The two main options are:

• Radiation therapy, which uses high-energy radiation to kill cancer cells
• Chemotherapy, which uses one or more anticancer drugs given through your veins, as a shot, or by mouth

Surgery may not make sense if the thymus cancer has already spread significantly since there isn’t a chance that this procedure will cure the cancer. However, surgery may still be an option to lessen symptoms.

Your medical team will recommend an approach based on your cancer’s characteristics, how much it has spread, and other factors like your overall health and your personal preferences.

Treatment for Cancer Recurrence

Unfortunately, thymus cancer comes back in some people (called recurrence), even after it has been successfully treated. This may happen if your treatment team couldn’t get rid of all the cancer cells in your body.

You might receive chemotherapy treatment for a cancer recurrence, potentially using a different kind of chemotherapy drug or drugs than you first received. 

Another kind of treatment, called biologic therapy, is also sometimes used in people with recurrent cancer. These treatments are more targeted than standard chemotherapy and work by stimulating your own immune system to kill cancer cells. Examples are Sutent (sunitinib) and Afinitor (everolimus).

Surgery and radiation are less commonly used, but they might make sense in particular situations. 

Follow-up Care

Even after your initial cancer treatment, you will need to keep seeing your healthcare provider regularly to look out for cancer recurrence. 

You may need follow-up blood tests or imaging scans for this. Your provider can also help monitor you for side effects from treatment, some of which may not appear for many years. 

Treatment for Autoimmune-Related Conditions

Some people also need treatment for autoimmune conditions related to their thymus cancer, such as myasthenia gravis. In some cases, the autoimmune condition will go away after the thymus is surgically removed. 

Thymus Cancer Prognosis

The success of treatment depends a lot on the subtype of cancer present, but perhaps even more on how much the cancer has spread. In general, the prognosis is worse as the category letters progress from A to C. 

For example, in people with a type A thymoma, almost everyone is living without cancer 10 years after diagnosis. In contrast, in someone with a B2 type-thymoma, around 70%–80% of people are living cancer-free in 10 years. 

People with thymic carcinoma tend to do worse than people who have thymoma. Of people diagnosed with thymic carcinoma, around 30%–50% will be alive five years later. 

The prognosis is also worse in people who have higher cancer staging. For example, someone diagnosed with stage 2 cancer has a much better chance of survival than someone with stage 4 cancer. 

Summary

Thymomas and thymic carcinomas are rare cancers of the thymus, an organ in your upper chest. Thymomas are more common and easier to treat than thymic carcinomas.

Surgery is the primary treatment for both thymomas and thymic carcinomas. If your cancer has not spread, it often cures the disease. Radiation and/or chemotherapy are sometimes used in addition to or instead of surgery.

Prognosis depends on a person’s stage and specific type of thymoma and thymic carcinoma. Rates of survival are lower for thymic carcinoma compared to thymoma. 

A Word From Verywell

Learning that you have any kind of cancer can be overwhelming. It’s easy to feel scared and lost in the information coming to you. Fortunately, many people with cancer of the thymus survive the disease and live long lives free of cancer. Work with your healthcare team to get the resources, information, the support that you need.