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Thymus

This information should not be used for self-diagnosis or in place of a qualified physician's care.

Reviewed March 2016

The basics
  • Guidelines for treating this cancer have been developed by the Lung Tumour Group.
  • For health professional information on treating this cancer, please see our Cancer Management Guidelines.
  • The thymus is a small organ inside the chest, behind the breastbone. It sits just in front of and above the heart and may extend to the root of the neck.
  • The thymus is large in infants. It grows until puberty and then gradually decreases in size during adulthood as it is replaced with fat.
  • The thymus is divided into two lobes that are surrounded by a thin layer of tissue.
  • The thymus is made up of two types of cells: epithelial cells and lymphocytes.
  • Epithelial cells are the cells that line the thymus, and are the cells of origin for thymic-related cancers such as thymoma and thymic carcinoma.
  • One of the thymus functions is to help control the immune system.
  • The thymus is part of the lymphatic system. T Lymphocytes are a type of white blood cell that develop in the thymus, especially in early life. These cells help protect the body from infections and viruses. If lymphocytes become cancerous, they can develop into lymphoma.
  • Thymus cancers have different names including thymomas, thymic carcinomas, thymic epithelial tumor or thymic carcinoid tumors.
  • Thymus cancers are very rare and may be difficult to diagnose and treat.

What causes it and who gets it?

Listed below are some of the known risk factors for this cancer. Not all of the risk factors below may cause this cancer, but they may be contributing factors.

  • The cause of thymus cancer is unknown.
  • Patients are usually between 40 and 60 years of age.
  • Men and women are equally affected.
  • Thymus cancer and myasthenia gravis (a chronic disease that causes muscle weakness) are often associated.
  • Statistics
    • These cancers are so uncommon that specific incidence rates are not available. Thymus cancer statistics are presented in combination with other unspecified cancers.
    • BC
    • Canada

Can I help to prevent it?

There is no known way to prevent thymus cancer.

Screening for this cancer

No effective screening program exists for this cancer yet.

Patients with myasthenia gravis are regularly checked for thymus cancer.

Signs and Symptoms

  • There are often no symptoms of thymus cancer.
  • If the growing tumour presses against other organs, the following chest symptoms may result:
    • coughing
    • shortness of breath
    • difficulty breathing (dyspnea)
    • difficulty swallowing (dysphagia)
    • chest tightness or pain
  • If the tumour presses on the vena cava (the great vessel that returns blood to the heart) the following symptoms might be noticed:
    • swelling in the neck and face
    • feeling light-headed
    • headaches
  • Advanced tumours may cause chest pain.
  • This cancer is sometimes accompanied by immune disorders and low red blood cell counts.
Diagnosis & staging

Diagnosis

These are tests that may be used to diagnose this type of cancer.

  • Tumours are often discovered through chest x-rays that have been done for unrelated reasons. 
  • A chest x-ray or CT Scan is used as a beginning assessment. 
  • Magnetic Resonance Imaging (MRI) may show if the tumour has spread.
  • A fine needle biopsy (removal and examination of a small bit of tissue) is essential for the definite diagnosis of thymus cancer.

For more information tests used to diagnose cancer, see our Recommended Websites, Diagnostic Tests section.

Types and Stages

Types

  • There are three main types of thymus cancer:
    • Thymoma (most common)
    • Thymic carcinoma (uncommon)
    • Thymic carcinoid tumour (least common)
Stages

Staging describes the extent of a cancer. The TNM classification system is used as the standard around the world. In general a lower number in each category means a better prognosis. The stage of the cancer is used to plan the treatment.  

T describes the site and size of the main tumour (primary) 

N describes involvement of lymph nodes 

M relates to whether the cancer has spread (presence or absence of distant metastases). 

Stage I
Intact capsule or growth within the capsule. (The capsule is the thin outer layer of the thymus). 

Stage II
Microscopic spread into the nearby fatty tissue or mediastinal pleura (thin layer covering the space between the two lungs).

Stage III
Visible spread into the nearby organs: lungs, great vessels, pericardium. 

Stage IV
Extensive spread within the chest or lymph nodes.
Treatment

Treatment

Cancer therapies can be highly individualized – your treatment may differ from what is described below. 

Surgery
  • The most effective treatment is the complete surgical removal (resection) of the tumour.
  • Patients with Stage I (intact) tumours that are completely removed by surgery, have no need for adjuvant radiotherapy.
Radiotherapy
  • Radiotherapy is given after surgery of invasive thymomas, and for all thymic carcinomas.
  • Adjuvant radiotherapy significantly reduces the recurrence rates for invasive tumours.
Chemotherapy
  • If the tumour has spread into nearby tissues, chemotherapy or chemoradiation may be given ahead of surgery to shrink the tumour.
  • Chemotherapy may be used for advanced stages or recurrent thymus cancer.
Prognosis
  • The majority of thymus cancer cases are curable.

Follow-up after Treatment

  • Guidelines for follow-up after treatment are covered on our website.
  • You will be returned to the care of your family doctor or specialist for regular follow-up. If you do not have a family physician, please discuss this with your BC Cancer oncologist or nurse.
  • Follow-up testing is based on your type of cancer and your individual circumstances.
  • Life after Cancer focuses on the issues that cancer survivors can face.
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