Metastasis is the spread of cancer cells from the original site to other parts of the body.
What is going on in the body?
When a tumour is malignant, or cancerous, it can spread from the initial site to other parts of the body. This often happens in two ways: through direct growth of the cancer or invasion of distant sites. Invading cells move through the lymph system. This is a system of narrow vessels similar to blood vessels. The system transports white blood cells and clear fluid, called lymphatic fluid. Cancer can also grow directly outward. This is called local extension.
When tumour cells spread to other areas of the body, it is called metastasis. As cancer grows and changes, cells lose their ability to stay in a single tumour mass. When cancer cells get into the lymph system or blood vessel system, they break off. Cells can spread as a single cell or as many tiny cells. The cells circulate until they find a good place to grow. The entire body is supplied by blood and drained by the lymph system. Metastases can appear in any part of the body. A site for metastatic cancer must have a blood supply and an environment where it can grow. Cancer cells may travel throughout the body. They only take hold in specific locations. Common sites are the brain, lungs, liver, lymph nodes, bone, skin, and adrenal glands.
Some cancers tend to involve the entire body or system from the start. Such cancers include leukaemias and lymphomas. Where and when a cancer will spread depends on the primary tissue type and the genetic abnormality of the cancer.
What are the signs and symptoms of the disease?
The symptoms of metastasis depend on the site of spread. In metastasis to the brain and central nervous system, symptoms include:
Tumours in the lungs can cause:
- blurred vision
- poor balance
- speech problems
- masses in lymph nodes
Liver metastasis can cause an enlarged painful liver, jaundice, or yellowing of the skin, loss of appetite, and elevated liver enzyme levels.
- coughing that produces blood
- low oxygen levels, called hypoxia
- dizzness from lack of oxygen
- shortness of breath
- fluid around the lungs
- chest pain
Other common problems are skin tumours, excess fluid in the abdomen, known as ascites, and swelling caused by blocked lymph vessels, called lymphoedema.
Failure of the bone marrow can lead to the blood having too few:
The adrenal gland may fail. The kidney or gallbladder ducts may become blocked. Many other symptoms are possible. These symptoms are not linked to a particular kind of cancer.
- red cells, which is called anaemia
- white cells, which is called leukopenia
- platelets, which is called thrombocytopenia
What are the causes and risks of the disease?
The particular genetic changes in the cancer may make it more prone to spread. Metastasis depends on how different the cancer is from surrounding tissue, whether or not certain genes are activated, and how close the cancer is to lymph or blood vessels. Other factors are the strength of the person's immune system, and how long a malignancy has gone untreated. Anyone with a malignancy is at risk for metastases. There are a few cancers that rarely spread. These include primary brain tumours and basal-cell or squamous-cell carcinoma of the skin.
What can be done to prevent the disease?
Prevention of metastasis depends on early diagnosis and treatment of cancer. Many people have tiny metastases that cannot be seen at the time of diagnosis. Treatments such as chemotherapy or radiation are used as treatment. The prevention and control of metastases is an active area of cancer research.
How is the disease diagnosed?
Diagnosis of tumour spread is done by physical examination and blood tests. X-rays and other imaging studies may help. Special X-rays, such as MRIs and CAT scans, may be used. These can find tumours smaller than 1/2 centimetre. Finding even smaller, microscopic metastases would be useful. Future tests may check for cancer genes in parts of the body where tiny metastases are suspected.
Some people are assumed to have microscopic metastasis because of the nature of the primary tumours. They are treated to try to overcome this problem. Sometimes the situation is unclear, and a biopsy may be needed. Testing can involve removal of a lymph node, needle puncture of a tumour, or examination of a bone marrow sample.
What are the long-term effects of the disease?
Some cancers with metastasis can be cured. These include tumours that are highly sensitive to radiation or chemotherapy. Some examples are:
People can live with metastases for many years. These cancers may include:
- thyroid cancer
- testicular and other germ-cell cancers
- some sarcomas
Metastasis usually leads to death if it cannot be removed or treated.
- breast cancer
- low-grade lymphoma and leukaemia
- low-grade sarcomas
- prostate cancer
What are the risks to others?
There is no risk to others.
What are the treatments for the disease?
Some metastases can be removed surgically. This depends on the type of cancer and its location. This is usually the case when there are very few metastases or the metastasis is isolated.
Medical treatment is the usual approach. Some cancers respond well and are curable, even if there are multiple metastases. Radiation can be useful for local tumour recurrence. Otherwise, systemic therapy is needed. This includes chemotherapy and immune-based therapy. These treatments are administered intravenously or orally. The drugs circulate in the body. These treat malignant cells wherever they are. Chemotherapy may be administered through an artery, or into the chest or abdominal cavities, an arm, or a leg.
Much research is being done on treating metastasis. Other approaches are being tried. These include anticoagulation of the blood, enzyme inhibitors, gene therapy, and growth factor inhibitors. These treatments are experimental.
What are the side effects of the treatments?
Some people can have more than one brain or lung metastasis removed without many long-term problems. Any surgery involves risks. These include infection, bleeding, scarring, loss of organ function, and death.
Radiation treatment for metastasis is usually directed to just one area. Any side effects will be related to the area being treated. In general, nausea, fatigue, and skin irritation can result. More serious effects, like bone marrow suppression or secondary cancers, are possible. Chemotherapy and immunotherapy have many side effects, depending on the drugs used. Side effects can be mild, such as nausea, temporary hair loss, and fatigue. More severe nausea and fatigue can be treated with new medications. Side effects can also be life-threatening, with severe infections, secondary tumours, severe blood clots, or organ toxicity.
What happens after treatment for the disease?
Some treatments have late complications and people need continued medical care.
How is the disease monitored?
The person is watched for any recurrence of metastases. Physical examinations, blood tests, and tests for tumour markers are done. Chest X-rays, CAT scans, bone scans, and MRIs may also be done. In some cases, regular biopsies are performed. Routine screening for remaining cancer genes is being studied.
Author: Thomas Fisher, MD
Reviewer: HealthAnswers Australia Medical Review Panel
Editor: Dr David Taylor, Chief Medical Officer HealthAnswers Australia
Last Updated: 1/10/2001
Potential conflict of interest information for reviewers available on request