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Thymomas and thymic carcinomas are tumours that affect the thymus gland. This information is about these types of tumours, their symptoms, diagnosis and possible treatments.
The thymus gland sits behind the breastbone in the chest cavity. It makes certain white blood cells called T lymphocytes, which are part of the body's immune system and help fight infection.
The thymus gland becomes fully developed around puberty and then gradually becomes less active and shrinks. It’s replaced by fat and scar tissue but the thymus continues to make T lymphocytes until old age.
Diagram showing the position of the thymus gland
View a large copy of the diagram showing the position of the thymus gland|
Cancer affecting the thymus gland is rare and the cause is unknown. This information is about thymoma and thymic carcinoma. However, other cancers can affect the thymus gland, such as lymphomas|, germ cell tumours and neuroendocrine tumours|. You can contact our cancer support specialists for further information about these.
Thymomas are rare. The most common age for people to be diagnosed with a thymoma is between 40 and 60 years. Thymomas tend to be benign (non-cancerous) and slow-growing but some can spread, mainly within the chest.
Thymic carcinoma is even rarer and can affect people of any age. It’s malignant (cancerous), fast-growing and may spread to other parts of the body.
Because the thymus gland is involved in the development of the immune system, some people with a thymus gland tumour will also have immune system-related illnesses.
One of these is a condition called myasthenia gravis. The main symptom of this is that muscles become tired and easily weakened.
As many as 4 out of every 10 people (40%) with a thymoma will also have myasthenia gravis. Thymic carcinoma is less commonly associated with myasthenia gravis.
Another associated condition is a type of anaemia called pure red cell aplasia. Anaemia means that there aren't enough red blood cells to carry oxygen around the body. It causes tiredness and sometimes breathlessness. Pure red cell aplasia affects about 1 out of every 20 people (5%) who have a thymus gland tumour.
Other conditions that may be associated with a thymus gland tumour include immune diseases of the nervous system or bowel, such as ulcerative colitis or Crohn's disease.
Symptoms of a thymus gland tumour include:
It is possible for a thymus gland tumour to be found following a chest x-ray for something else, even if the person has no symptoms.
Finding that a person has an autoimmune system disease such as myasthenia gravis may lead a doctor to suspect and carry out tests for a thymus gland tumour.
Some people with a later stage disease may have reduced immunity and so be more likely to develop infection.
Usually you begin by seeing your GP, who will examine you. They will refer you to a hospital specialist for any tests that may be necessary and for expert advice and treatment.
The doctor at the hospital will ask you about your general health and any previous medical problems before examining you. They may arrange blood tests to check your general health and to test for any associated conditions, such as myasthenia gravis.
The following tests are commonly used to diagnose thymus gland tumours:
A chest x-ray will be taken to check for any abnormalities in your thymus gland. Up to half of all thymus gland tumours are detected on a chest x-ray.
A CT scan takes a series of x-rays that build up a three-dimensional picture of the inside of the body. The scan is painless and takes 10–30 minutes. CT scans use a small amount of radiation, which will be very unlikely to harm you and will not harm anyone you come into contact with. You will be asked not to eat or drink for at least four hours before the scan.
You may be given a drink or injection of a dye, which allows particular areas to be seen more clearly. This may make you feel hot all over for a few minutes. If you’re allergic to iodine or have asthma, you could have a more serious reaction to the injection, so it’s important to let your doctor know beforehand.
This test is similar to a CT scan but uses magnetism instead of x-rays to build up a detailed picture of areas of your body. Before the scan you may be asked to complete and sign a checklist. This is to make sure that it’s safe for you to have an MRI scan.
Before having the scan, you’ll be asked to remove any metal belongings, including jewellery. Some people are given an injection of dye into a vein in the arm. This is called a contrast medium and can help the images from the scan to show up more clearly. During the test you will be asked to lie very still on a couch inside a long cylinder (tube) for about 30 minutes. It's painless but can be slightly uncomfortable, and some people feel a bit claustrophobic during the scan. It’s also noisy, but you’ll be given earplugs or headphones.
This uses low-dose radioactive sugar to measure the activity of cells in different parts of the body. A very small amount of a mildly radioactive substance is injected into a vein, usually in your arm. A scan is then taken a couple of hours later. Areas of cancer are usually more active than surrounding tissue and show up on the scan. Sometimes a type of scan that combines a CT scan and a PET scan may be used, as it can give more information about the position and size of a tumour.
A small sample of cells may be taken from the tumour and examined under a microscope. The area is numbed with local anaesthetic. A needle is inserted into the tumour (often at the same time as a CT scan) and cells are taken. A needle biopsy may not always be necessary.
If it’s not possible to get a sample of cells using a needle biopsy, very occasionally a mediastinoscopy may be needed. The doctor makes a cut about two inches long on the front of the chest. The doctor passes a tube with a light and camera on it through the cut. The camera helps the doctor see any abnormalities in the thymus gland and biopsies can also be taken. This test is done using a general anaesthetic.
This test is only sometimes needed. It involves making a small cut in the skin and inserting a tube with a light and tiny camera on it into another part of your chest. The camera helps the doctors look directly at the cancer and they may also take a sample of the cells, known as a biopsy. The cells from the sample are taken to a laboratory and looked at under a microscope to see if they are cancerous. This is done using a general anaesthetic.
It takes a while to process these tests and you may have to wait several days for the results. This is likely to be a very worrying time for you and it may help to talk to one of our cancer support specialists|.
The stage of a tumour describes its size and whether it has spread beyond its original site. Knowing the stage helps doctors to decide on the most appropriate treatment.
These can be categorised as non-invasive (stage 1) or invasive (stage 2–4).
Thymomas tend to be slow-growing and if they spread at all, it’s usually into nearby structures.
Thymic carcniomas tend to be more invasive and can spread further to other parts of the body. They can spread either in the bloodstream or through the lymphatic system. The lymphatic system is part of the body's defence against infection and disease. It’s made up of a network of lymph glands or nodes that are linked by fine ducts containing lymph fluid. Doctors will usually look at the nearby lymph nodes to find the stage of the cancer.
The tumour is confined to the thymus gland only.
The tumour has spread through the outer lining of the thymus gland or into the fat surrounding it, but has not spread to nearby lymph nodes or organs.
The cancer has spread into nearby organs such as the lungs, the lining of the heart (pericardium) and the blood vessels.
The cancer has spread widely into the lining of the lungs (pleura) and the lining of the heart (pericardium).
The cancer has spread through the blood and lymphatic system to other organs, such as the liver.
Grading refers to the appearance of the cancer cells under a microscope.
The thymus gland has a medulla and a cortex, which contain different types of cell. The medulla has more spindle cells (named after their shape) and the cortex has more epithelial cells (which line organs and cavities of the body). Doctors look at the tumour under the microscope and, depending on which type of cells they see, class the thymoma as 'medullary' or 'cortical'. Sometimes, if there are both spindle and epithelial cells, the tumour is classed as 'mixed'.
The World Health Organisation (WHO) classifies thymus gland tumours according to the grade and type:
Types A and AB are considered to be non-cancerous (benign). Types B1 to B3 are classed as low-grade (slow-growing), on the borderline between being benign or malignant. Type C is definitely cancer.
Type B2, cortical thymoma, is most commonly associated with myasthenia gravis.
Knowing the type and grade of thymoma or thymic carcinoma helps doctors to plan treatment.
The main treatment for thymus tumours is surgery|. Chemotherapy|, radiotherapy| or a combination of both may also be used.
Sometimes chemotherapy is given before surgery or radiotherapy to reduce the size of very large tumours. This can help make treatment more successful. Giving chemotherapy in this way is called neo-adjuvant chemotherapy.
As well as seeing a cancer specialist, you may be referred to a specialist in treating conditions of the brain and nervous system (a neurologist), for advice and treatment of myasthenia gravis. Also, because the thymus gland is part of the body's immune system, you may also be seen by a specialist in treating immune conditions.
It’s usually possible to remove the whole tumour if it’s contained within the thymus gland (encapsulated). If you have stage 1 thymoma, which is completely removed by surgery, no further treatment will usually be necessary.
Sometimes thymus gland tumours can spread into nearby structures. However, the full extent of the tumour can often only be accurately assessed during surgery.
You may need to have your thymus gland removed. This is known as a thymectomy. It is a major operation and involves making a cut through the breastbone (sternum).
Radiotherapy uses high-energy rays to destroy cancer cells, while doing as little harm as possible to healthy cells. If you have surgery but the cancer cannot be removed completely, or if the cancer is large, you may be offered radiotherapy.
If surgery is successful, you may be given radiotherapy to reduce the chance of the cancer coming back.
Radiotherapy can also be used to shrink the tumour before surgery, which may make the surgery more successful.
Chemotherapy is the use of anti-cancer drugs to destroy cancer cells. It is sometimes used if the tumour has spread, or if surgery and/or radiotherapy have not been successful. Thymus gland cancers can respond very well to chemotherapy. Often, a combination of chemotherapy drugs will be used.
Cancer research trials are carried out to try to find new and better treatments for cancer. Trials that are carried out on patients are known as clinical trials|.
Trials are the only reliable way to find out if a different operation, type of chemotherapy, radiotherapy, or other treatment is better than what is already available. You may be asked to take part in a treatment research trial. There can be many benefits in doing this.
Trials help to improve knowledge about cancer and the development of new treatments. You will also be carefully monitored during and after the study.
Because thymus gland cancer is very rare, however, there may not always be a relevant trial in progress.
During your diagnosis and treatment you are likely to experience a number of different emotions|, from shock and disbelief to fear and anger. At times these emotions can be overwhelming and hard to control. This is natural and it is important to be able to express them.
Everyone has their own ways of coping with difficult situations; some people find it helpful to talk to family or friends, while others prefer to seek help from people outside their situation. Others prefer to keep their feelings to themselves. There is no right or wrong way to cope, but help is available if you need it. If you would like further support, you can contact our cancer support specialists.
This information has been compiled using a number of reliable sources, including:
With thanks to Dr David Gilligan, Consultant Oncologist: and the people affected by cancer who reviewed this edition. Reviewing information is just one of the ways you could help when you join our Cancer Voices network|.
Content last reviewed: 1 January 2013
Next planned review: 2015
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© Macmillan Cancer Support 2013
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