Thymoma and thymic carcinoma
The thymus gland
The thymus gland lies in the centre of the chest behind the breast bone. It makes special white blood cells called T lymphocytes. These cells are part of the body’s immune system and help to fight infection. The thymus gland becomes fully developed around puberty and then gradually stops working and shrinks, being replaced by fat and scar tissue.
Thymoma and thymic carcinoma
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, such as lymphomas, germ cell tumours and neuroendocrine tumours.
Thymomas are rare. The commonest age for people to be diagnosed with a thymoma is between 40 and 60 years. They tend to be benign (non-cancerous) and slow growing.
Thymic carcinoma is even rarer and can affect people of any age. It is malignant (cancerous), faster growing and may spread to other parts of the body.
Associated conditions
Because the thymus gland is involved in the development of the immune system, some people with a thymus gland tumour will also have an immune system related illness.
The most common of these is a condition called myasthenia gravis. The main symptom of this is that muscles become tired and easily weakened. As many as 35% (35 in 100) of people with a thymoma will also have myasthenia gravis and approximately 15% (15 in 100) of people with myasthenia gravis have a thymoma.
Thymic carcinoma is not usually associated with myasthenia gravis.
Another associated condition is pure red cell aplasia. This causes the body to produce a very low number of red blood cells, resulting in a type of anaemia called pure red cell aplasia. Anaemia means that there are not enough red blood cells to carry oxygen around the body. It causes tiredness and sometimes breathlessness. Pure red cell aplasia affects about 5% (1 in 20) of people who have a thymus gland tumour.
Symptoms
Symptoms of a thymus gland tumour include:
- chest pain
- a persistent cough
- shortness of breath
- difficulty swallowing
- hoarseness of the voice
- swelling of the neck due to the tumour pressing on blood vessels in the chest – this is called superior vena cava obstruction (SVCO).
It is possible for a thymus gland tumour to be found following a chest x-ray for something else, when the person has no symptoms.
Diagnosis
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 take your full medical history, do a physical examination and take blood samples 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 a half of all thymus gland tumours are detected on a chest x-ray.
CT (computerised tomography) scan A CT scan takes a series of x-rays, which are fed into a computer to give a detailed picture of the chest. The scan can show whether the cancer has spread to other parts of the body. It is painless and takes around 10–30 minutes.
MRI (magnetic resonance imaging) scan This test is similar to a CT scan but uses magnetism instead of x-rays to form a series of cross-sectional pictures of the inside of the body. During the test you will be asked to lie very still on a couch inside a metal cylinder. The test can take up to an hour and is completely painless, although the machine is quite noisy. If you don’t like enclosed spaces you may find the machine claustrophobic.
Needle biopsy 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.
Mediastinoscopy If it is not possible to get a sample of cells using a needle biopsy, a small cut (known as a mediastinotomy) can be made in the skin at the base of the neck and a tube passed into the chest. The tube has a light and camera at the end and can magnify the areas it looks at. The doctor can see any abnormalities and may also take biopsies to examine under a microscope. This is done using a general anaesthetic.
Thoracoscopy This is similar to a mediastinoscopy. It involves making a small cut in the skin and inserting a tiny camera (as described above) into another part of your chest to look directly at the cancer and take samples from it.
It takes a little 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 the Cancerbackup nurses.
Staging
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.
Thymus tumours can be catergorised as non-invasive (stage 1) or invasive (stage 2–4). Thymomas tend to be slow-growing and, if they spread at all, it is usually into nearby structures.
Thymic carcinomas tend to be more invasive and can spread further, to other parts of the body.
Carcinomas can spread in the body, either in the bloodstream or through the lymphatic system. The lymphatic system is part of the body’s defence against infection and disease. It is 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.
- Stage 1 The tumour is confined to the thymus gland only.
- Stage 2 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.
- Stage 3 The cancer has spread into nearby organs such as the lung, the lining of the heart (pericardium) and the blood vessels.
- Stage 4 A The cancer has spread widely into the tissues around the lungs and heart
- Stage 4 B The cancer has spread through the blood and lymphatic system to other organs, such as the liver.
Grade and type
Grading refers to the appearance of the cancer cells under the microscope. The thymus gland has a medulla and a cortex which contain different types of cell. The medulla has more spindle cells and the cortex has more epithelial cells. Doctors look at the tumour under the microscope and, depending on which type of cells they see; they 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.
- A Medullary thymoma
- AB Mixed thymoma
- B1 Mainly cortical thymoma
- B2 Cortical thymoma
- B3 Thymic carcinoma
- C Thymic carcinoma – high grade (malignant)
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.
Knowing the type and grade of thymoma/thymic carcinoma helps doctors to plan treatment.
Treatment
The main treatment for thymus tumours is surgery. Chemotherapy, radiotherapy, or a combination of both may also be used.
Surgery
Complete surgical removal is usually possible if the tumour is 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.
Radiotherapy
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 is large) you may be offered radiotherapy.
If surgery is successful, but there is a possibility that the cancer will return (stage 2–4), you may be given radiotherapy to reduce the chance of this happening.
Radiotherapy can also be used to shrink the tumour before surgery, which may make the surgery more successful.
Chemotherapy
Chemotherapy is the use of anti-cancer drugs to destroy cancer cells. It is sometimes used if the tumour has spread more widely; 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.
Some people may have chemotherapy before surgery or radiotherapy to reduce the size of the tumour. This can help to make treatment more successful.
Research – clinical trials
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. However, because thymus gland cancer is very rare there may not always be a relevant trial in progress.
Your feelings
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 quite 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 friends or family, 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.
