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What is thymoma?

Thymoma is an uncommon type of tumor that grows in the thymus, a small organ just behind the breastbone (sternum). The thymus produces lymphocytes, a type of white blood cell that fights infections.

Thymic carcinoma is a rare type of thymus gland cancer. It usually spreads, has a high risk of recurrence, and has a poor survival rate. Thymic carcinoma is divided into subtypes, depending on the types of cells in which the cancer began.

The organ also contains epithelial cells and hormone-releasing Kulchitsky (neuroendocrine) cells, with several types of cancer possible:

  • Epithelial C – Thymoma (slow-growing) or thymic carcinomas (much rarer but harder to treat and more likely to spread to the lungs)
  • Kulchitsky cells – Carcinoid tumors (extremely rare)
  • Lymphocytes – Hodgkin Lymphoma and Non-Hodgkin Lymphoma

Given the cancer variations that can develop in the thymus, it’s important that a medical team with diagnostic expertise examines potential problems.

Many patients with thymoma are also diagnosed with one of the autoimmune disorders known as paraneoplastic syndromes, though researchers do not believe the cancer causes the conditions. Other patients may have one of the syndromes but never develop thymoma.

Paraneoplastic syndromes linked to thymoma include:

  • Myasthenia gravis (MG) – This disease is the most common disorder connected to thymoma, causing weakness in muscles under conscious control, such as those used in moving the eyes, chewing and making facial expressions. In severe cases, breathing and arm and leg control are also compromised. Approximately one-third to two-thirds of patients with thymoma have the disorder. It can appear before the cancer or develop during or after treatment.
  • Red cell aplasia – This disorder severely limits red blood cell production, and affects 5 percent of thymoma patients.
  • Hypogammaglobulinemia – This disorder causes levels of infection-fighting antibodies (gamma globulins) to drop. It develops in 5 to 10 percent of thymoma patients.


Sometimes thymoma and thymic carcinoma do not cause noticeable problems, and the cancers may show up on a chest X-ray or CT (CAT) scan given for other reasons. But other patients may experience one or more of these symptoms:

  • A persistent cough
  • Shortness of breath
  • Pain or pressure in the chest
  • Muscle weakness
  • Drooping eyelids
  • Double vision
  • Arm or facial swelling
  • Difficulty swallowing
  • Anemia (low red blood cell count)
  • Frequent infections
  • Fatigue
  • Dizziness

Just because someone has these symptoms doesn’t necessarily mean they have cancer. A doctor can determine what is causing symptoms.

Risk factors

There are no known risk factors for thymoma, though doctors and researchers continue to study the disease. Researchers have identified several DNA changes in patients who have cancer, but it’s still unclear what role, if any, they play in the disease’s development.


Thymoma is often diagnosed if someone is experiencing problems associated with the related conditions myasthenia gravis, hypogammaglobulinemia or red cell aplasia.

Diagnosis of thymoma or thymic carcinoma could also come from:

Physical exams – Giving doctors a chance to feel for “fullness” in the lower neck or other warning signs
Blood tests – Providing a clue by identifying any related autoimmune disorders
X-ray – An image of the body that allows the physician to see certain structures
CT (CAT) scan – Overlapping X-rays from different angles, with dye sometimes injected into veins or swallowed to allow doctors to see delicate, tiny structures
PET (positron emission tomography) scan – Injecting glucose (sugar) into the veins and using a rotating scanner to look for malignant cells throughout the body, not just at the origin site of the cancer (where it first started to grow)
MRI (magnetic resonance imaging) – Using a magnet, radio waves and a computer to take detailed pictures of the inside of the body
Biopsy – Removing cells or tissue and examining them with a microscope
Surgery – Removing a tumor without initial biopsy because of strong signs of cancer