Overview

Thymic epithelial tumours

Thymic epithelial tumours occur when cancer (malignant) cells form on the outside surface of the thymus.

The thymus

The thymus is a gland in the chest, behind the breastbone (sternum). It is involved in the development of white blood cells called lymphocytes. These cells help to fight infection as part of the body’s immune system. It is at its largest in adolescence and then gradually shrinks away throughout adulthood, being replaced with fatty tissue.  

About thymic epithelial tumours

Thymic epithelial tumours are rare and the cause is unknown. 

There are 2 types:

  • Thymoma
  • Thymic carcinoma

Thymoma

Thymomas are typically slow-growing tumours that look similar to normal cells of thymus. However, they can vary in how they behave, and spread to the lungs or lining of the lungs (pleura). It is unusual for them to spread anywhere else in the body.

Some people diagnosed with thymoma also have an immune system condition (autoimmune disorder). This affects their body’s ability to fight infection.

The following conditions are linked to thymoma.

  • The most common condition linked to thymoma is called myasthenia gravis. The main symptom of this is that the muscles become weak and tired.
  • Hypoglobulinaemia is another rare condition linked to thymoma. People with hypoglobulinaemia have very low levels of antibodies in the blood. This leads to an increased risk of infection. Antibodies help the body to fight bacteria and viruses.
  • Pure red cell aplasia stops the body making enough red blood cells. The red blood cells carry oxygen around the body.

Symptoms

Symptoms of thymoma can include: 

  • chest pain
  • a persistent cough
  • becoming breathless or wheezy
  • difficulty swallowing
  • a hoarse voice

Sometimes thymoma has no symptoms and is found during tests for something else. 

Thymic carcinoma

Thymic carcinoma is much rarer than thymoma. It tends to grow and develop more quickly, and is more likely to spread to other parts of the body.

Unfortunately, this can make thymic carcinoma more difficult to treat. 

Resource number: 4348/VER3
Last reviewed: January 2025
Next review due: January 2028 

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