Cancer is made of changed cells that grow out of control. The changed (abnormal) cells often grow to form a lump or mass called a tumor. Cancer cells can also grow into (invade) nearby areas. And they can spread to other parts of the body. This is called metastasis.

The thymus is a small organ in the front part of your chest under the top part of the breastbone. It's an important part of your immune system. The thymus makes white blood cells called lymphocytes. They protect you against viral and bacterial infections.

Thymus cancer is a rare cancer that starts in the cells that make up the thymus. There are two main types of thymus tumors:

• Thymoma. The cancer cells look a lot like normal cells of the thymus. They grow slowly and rarely spread.
• Thymic carcinoma. The cancer cells do not look like normal cells of the thymus. They grow quickly and are more likely to spread to other parts of the body.

A risk factor is anything that may increase your chance of having a disease. The exact cause of someone's cancer may not be known. But risk factors can make it more likely for a person to have cancer. Some risk factors may not be in your control. But others may be things you can change.

Thymus cancer is rare. But anyone can get it. Only a few factors are known to increase risk for thymus cancer, and they aren't under your control. The risk factors are:

• Older age.
• Being Asian American or a Pacific Islander.

Thymus cancer doesn't seem to be linked to family history. This means the risk isn't inherited from your parents. No environmental or lifestyle factors are known to increase thymus cancer risk.

There is no known way to prevent thymus cancer.

There are no regular screening tests for thymus cancer. Screening tests are done to check for disease in people who don't have symptoms.

Thymus cancer may not cause symptoms unless the tumor grows large enough to press on nearby organs or blood vessels in your chest. If this happens, symptoms can include:

• A cough that doesn't go away or gets worse over time.
• Chest pain.
• Shortness of breath.
• Trouble swallowing.
• Loss of appetite.
• Unexplained weight loss.
• Tiredness.
• Muscle weakness.
• Swelling in your face and arms.
• Lightheadedness or dizziness.
• Headaches.
• Drooping eyelids.
• Double vision.
• Anemia, which is a low red blood cell count.
• Frequent infections.

Many people with a thymus tumor also develop an autoimmune disease, most often myasthenia gravis. This may be the first sign of thymus cancer.

Many of these symptoms may be caused by other health problems. But it's important to see your doctor if you have these symptoms. Only a doctor can tell if you have cancer.

Sometimes a thymus tumor is found by an imaging test of the chest that's done for another reason. If your doctor thinks you may have thymus cancer, they will ask you about your health history, symptoms, risk factors, and family history of disease. A physical exam will be done. You may also have:

• A chest X-ray.
• Other imaging scans such as a CT scan, PET scan, or MRI.
• Blood tests.

Unlike many other types of cancer, a biopsy isn't always needed to diagnose thymus cancer before surgery. This is because imaging tests can often show that cancer is most likely present. A diagnosis of thymus cancer is then confirmed at the time of surgery. At that time, the surgeon removes the tumor and sends it to a lab. In the lab, a pathologist looks at the removed tissues to check for cancer cells.

After a diagnosis of thymus cancer, you'll likely have other tests. These help your doctors learn more about your cancer. They can help find out the stage of the cancer. The stage is how much and how far the cancer has spread (metastasized) in your body. It is one of the most important things to know when deciding how to treat the cancer.

After your cancer is staged, your doctor will talk with you about what the stage means for your treatment. Be sure to ask your doctor to explain the stage of your cancer. Don't hesitate to ask questions. Consider writing your questions down and bringing them with you when you meet with your doctor. This will help make sure that you won't forget to ask about something.

Your treatment choices depend on the type of thymus cancer you have, test results, and the stage of the cancer. The goal of treatment may be to cure you, control the cancer, or to help ease problems caused by cancer. Talk with your care team about your treatment choices, and what the risks and side effects may be.

Types of treatment for cancer are either local or systemic. Local treatments remove, destroy, or control cancer cells in one area. Surgery and radiation are local treatments. Systemic treatment is used to destroy or control cancer cells that may have traveled around your body. When taken by pill or injection, chemotherapy is a systemic treatment. You may have one treatment or a combination of treatments.

Thymus cancer may be treated with:

• Surgery.
• Radiation therapy.
• Chemotherapy (chemo).
• Hormone therapy.
• Targeted therapy.

Talk with your doctors about your treatment choices. Make a list of questions. Think about the benefits and possible side effects of each choice. Talk about your concerns with your doctor before making a decision.

Cancer treatment, such as chemotherapy and radiation, can damage normal cells. This can cause side effects, such as hair loss, mouth sores, and vomiting.

Talk with your doctor about side effects or long-term side effects that you might have and about ways to manage them. There may be things you can do and medicines you can take to help prevent or control side effects.

Many people feel worried, depressed, and stressed when dealing with cancer. Getting treatment for cancer can be hard on your mind and body. Keep talking with your care team about any problems or concerns you may have. Work together to ease the effect of cancer, treatments, and its symptoms on your daily life.

Here are tips:

• Talk with your family or friends.
• Ask your care team or social worker for help.
• Speak with a counselor.
• Talk with a spiritual advisor, such as a minister or rabbi.
• Ask your care team about medicines for depression or anxiety.
• Keep socially active.
• Join a cancer support group.

Cancer treatment is also hard on the body. To help yourself stay healthier, try to:

• Eat healthy foods, with a focus on high-protein, high-calorie foods, fruits, and vegetables.
• Drink plenty of water, fruit juices, and other liquids.
• Keep physically active.
• Rest as much as needed.
• Talk with your care team about ways to manage treatment side effects.
• Take your medicines as directed by your team.

Your doctor will talk with you about when to contact them. You may be told to contact them if you have:

• New symptoms or symptoms that get worse.
• Signs of an infection, such as a fever.
• Side effects of treatment that affect your daily function or don't get better with treatment.

Ask your doctor what signs to watch for and when to contact them. Know how to get help after office hours and on weekends and holidays.

Tips to help you get the most from a visit to your doctor:

• Know the reason for your visit and what you want to happen.
• Before your visit, write down questions you want answered.
• Bring someone with you to help you ask questions and remember what your doctor tells you.
• At the visit, write down the name of a new diagnosis, and any new medicines, treatments, or tests. Also write down any new directions your doctor gives you.
• Know why a new medicine or treatment is prescribed, and how it will help you. Also know what the side effects are and when they should be reported.
• Ask if your condition can be treated in other ways.
• Know why a test or procedure is recommended and what the results could mean.
• Know what to expect if you do not take the medicine or have the test or procedure.
• If you have a follow-up appointment, write down the date, time, and purpose for that visit.
• Know how you can contact your doctor if you have questions, especially after office hours or on weekends.