Cancer happens when cells in the body start changing and growing out of control. These cells can form lumps called tumors. Thymoma and thymic carcinoma are two types of cancer that start in the cells of the thymus. These types of cancer are rare.

The thymus is an organ in the middle of the top of your chest, under your breastbone (sternum). It's part of the lymphatic system. The lymphatic system helps you fight illnesses. The thymus helps make white blood cells called T-lymphocytes (T-cells) that travel to lymph nodes. The thymus is most active when you're a child. It shrinks as you get older.

Epithelial cells line the thymus. Cancer can start to grow in these cells. There are two main types of cancer that can grow in the thymus cells:

• Thymoma. This is a tumor that tends to grow slowly. In some cases, these cancer cells can spread to the lining of the lungs (pleura). This type of cancer is easier to treat and cure.
• Thymic carcinoma. These are cancer cells that grow faster. This type is more likely to spread to other parts of the body. It can be harder to treat.

Many people with thymoma may also have an autoimmune disease. These types of diseases cause the immune system to attack the body's own tissues. People with thymoma may have a disease called myasthenia gravis. Or they may have another disease such as systemic lupus erythematosus, Sjögren's syndrome, or rheumatoid arthritis. Talk with your care team about testing and treatment for autoimmune diseases.

Some people don't have symptoms. Symptoms can be caused by the tumor pressing on nearby structures, such as the airway or the large blood vessel called the superior vena cava. You may have symptoms such as:

• A cough that doesn't go away.
• Feeling short of breath.
• Pain in your chest.
• A hoarse voice.
• Feeling pressure in your chest.
• Swelling in your arms, face, neck, or upper body.
• Tiredness.
• Dizziness.
• Trouble swallowing.
• Weak muscles.
• Drooping eyelids.
• Double vision.

Your doctor will ask about your symptoms. You'll also have one or more of these tests:

• Chest CT scan. This test uses a series of X-rays from several angles and a computer to make detailed images of the inside of the chest. It can be used to measure the size of the tumor. During the test, you may receive contrast given into a vein or by mouth. This will make parts of your body show up better in the image. If you can't have a chest CT with contrast, an MRI may be done instead. A chest CT is a commonly used test to diagnose a thymic tumor.
• MRI. This test uses strong magnets and a computer to make images of the inside of the body. Contrast is given into a vein before the scan.
• Positron emission tomography (PET) scan or PET-CT. This test uses a fluid injected into a vein and a special camera to find fast-growing cells in the body. The fluid contains a small amount of sugar with radiation. A PET scan is often combined with a CT scan (PET-CT scan). This allows areas that show up on the PET scan to be compared with the more detailed image of the CT scan. This test can show if cancer cells have spread to other parts of the body.
• Biopsy. A small piece of tissue is taken from the tumor. This may be done with a thin needle put through the skin of the chest. Or a cut may be made next to the sternum. A little piece of tumor is removed through this cut. The cells are examined in a lab by a doctor called a pathologist. You may have a biopsy depending on the results of the imaging tests. A biopsy can help your doctor find out if you have cancer.

Diagnostic tests help your doctors figure out the stage of the cancer. The stage is how much and how far the cancer has spread (metastasized) in your body. It's 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. Ask your doctor to explain the stage of your cancer. Sometimes the tumor may be diagnosed, staged, and treated when you have surgery.

The type of treatment you get depends on things like the type of cancer, if it has spread to other parts of your body, your preferences, and what risks and side effects are acceptable to you. Talk with your doctor about how much time you can take to explore your treatment options. You may want to involve your partner, spouse, family, or friends in this process. Make a list of questions for your doctor. Consider the benefits and possible side effects of each option. Discuss your concerns with your doctor.

The most common treatment is surgery. This is done to remove the tumor and some of the healthy surrounding tissue. The surgery is usually done by a thoracic surgeon who specializes in chest surgery.

In addition to surgery, you may also have one or more of these:

• Radiation therapy. This uses high-energy X-rays to kill cancer cells.
• Chemotherapy. This is medicine to stop cancer cells from growing. It can kill cells that have spread to other parts of the body. You may be given one medicine or a combination of medicines.
• Immunotherapy. This kind of treatment uses medicines to help the immune system kill cancer cells.
• Targeted therapy. This treatment uses medicines that help target specific things the cancer needs to grow and spread.

Researchers are always looking for new ways to treat cancer. These new methods are tested in clinical trials. Clinical trials are done to see if the new treatment works well or is even better than the standard treatment. Before starting treatment, ask your doctor if there are any clinical trials you should think about.

Both types of cancer can come back after treatment. Thymic carcinoma is more likely to come back. After either type of cancer, you are at a higher risk of having another type of cancer in the future. You'll need regular follow-up visits to check for new cancer. Talk with your care team about when to schedule visits and testing.

Contact your doctor if you have:

• A fever of 100.4°F (38°C) or higher, or as directed by your doctor.
• Pain that gets worse.
• Symptoms that don't get better, or that get worse.
• New symptoms.