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Thymoma is a rare cancer that affects the thymus gland, an organ located between the lungs. As part of the immune and lymphatic systems, the thymus supports the immune system's development during childhood and helps the body fight illness throughout life.

A thymoma originates in the epithelial cells lining the thymus. (Epithelial cells are tightly packed cells that cover surfaces of organs and other body parts.) This tumor typically grows slowly and is unlikely to spread. In some cases, however, cancer cells spread to the lining of the heart and lungs or to other tissues throughout the body. Another cancer of the thymus, thymic carcinoma, tends to grow faster than thymoma and is more likely to spread, or metastasize.

While the exact cause of thymoma is unknown, it is common in patients with myasthenia gravis, an autoimmune disorder that causes muscle weakness. Thymoma affects men and women equally and is typically diagnosed in patients over 70.

Our approach to thymoma

UCSF's highly skilled thoracic oncologists and thoracic surgeons deliver state-of-the-art care for patients with thymoma. Our team will provide a precise diagnosis and a tailored treatment plan, which may include surgery, radiation, chemotherapy, hormone therapy, targeted therapy, immunotherapy or other cutting-edge therapies. In the operating room, we use minimally invasive techniques, such as robot-assisted surgery, which can decrease complications and improve results. Our patients can also bolster their recovery and overall wellness by accessing continued care and support services, including support groups, nutrition education and mental health care.

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Signs & symptoms

Up to 50% of thymomas do not cause symptoms. Patients who do have symptoms may experience:

  • Chest pain
  • Shortness of breath
  • Coughing
  • Swelling in the face, neck, arms or elsewhere in the upper body

Less common symptoms include fever, night sweats and weight loss.


Your doctor will start by conducting a physical exam, reviewing your medical history and evaluating your symptoms. The next step will be one of the following tests:

  • Chest X-ray. Most thymomas can be detected in a traditional chest X-ray, but your doctor may order additional imaging tests for more details about the tumor's size, location and composition.
  • Chest CT scan. To take images, a thin X-ray beam rotates around the chest area; then a computer program processes the data to construct a three-dimensional, cross-sectional image.
  • PET scan. This highly sensitive technique uses a radioactive tracer to collect images of body tissues.
  • Chest MRI scan. A powerful magnet linked to a computer is used to create detailed images of structures inside the body.
  • Biopsy. If imaging tests reveal a tumor, your doctor may conduct a biopsy to confirm the diagnosis of thymoma. This involves using a needle or surgical procedure to collect a tissue sample that can be examined in the laboratory.


If the diagnosis is thymoma, your doctor will want to determine the stage or extent of the disease. Staging is a careful process to learn whether cancer has spread and, if so, to which parts of the body. Knowing the stage helps doctors plan treatment. The four stages of thymoma are described below:

  • Stage I. The tumor is confined to the thymus gland.
  • Stage II. Cancer cells have spread to the fat around the thymus or to the lining of the chest cavity.
  • Stage III. Cancer cells have spread to nearby organs, such as the lungs, sac surrounding the heart, or large blood vessels.
  • Stage IV. Cancer cells have metastasized throughout the heart, lungs, blood or lymphatic system.


How thymoma is treated depends on whether it has spread and its stage, but patients typically undergo one or more of the following:

  • Surgery. Removing the tumor is the most common treatment for thymoma. In early stages, when cancer cells haven't spread beyond the thymus, surgery may be all that's needed.
  • Radiation therapy. Also called radiotherapy, this involves using high-energy X-rays to kill cancer cells. Radiation therapy is restricted to a limited area and affects the cancer cells only in that area. It may be used before surgery to shrink a tumor or after surgery to destroy any remaining cancer cells in the treated area.
  • Chemotherapy. This is the use of anticancer drugs to kill cancer cells throughout the body. Chemotherapy is typically used for thymomas that have spread beyond the thymus. The drugs may be delivered orally (as pills) or directly into the circulation (through an IV injection or catheter).
  • Hormone therapy. This can slow the growth of cancer cells by removing or blocking the activity of hormones. In later stages of thymoma, corticosteroids may be used to limit the cancer's spread.
  • Targeted therapy. Drugs or other substances are used to pinpoint and attack specific types of cancer cells (for instance, the therapy may block molecules that stimulate tumor growth). Your doctor may run tests to determine the genetic or molecular makeup of your tumor – information that can guide treatment choices. Targeted therapies tend to cause less damage to healthy cells than does chemotherapy or radiation.
  • Immunotherapy. This treatment leverages the patient's own immune system to treat thymoma. Substances are used to mobilize the body's natural defenses to kill cancer cells or prevent them from spreading.

UCSF Health medical specialists have reviewed this information. It is for educational purposes only and is not intended to replace the advice of your doctor or other health care provider. We encourage you to discuss any questions or concerns you may have with your provider.

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