Cancer can start in any organ or tissue in the body. A primary cancer or tumour is the first, original tumour that develops in the body. Metastatic cancer occurs when cancer spreads from its original location (primary tumour) to a new part of the body. Metastatic tumours always start from cancer cells in another part of the body. For example, breast cancer can spread from its primary site (the breast) to form a new tumour in a different part of the body, such as the bones. The cancer cells in this second tumour are the same as the cells in the primary tumour – they are breast cancer cells, and not bone cancer cells. When this happens, it is called metastatic breast cancer, and not bone cancer.
Metastatic cancer may also be called:
- a secondary tumour or cancer
- metastasis (singular)
- metastases (plural)
How cancer spreads
As cancer cells divide, they can invade and grow directly into surrounding tissue or structures (direct extension). But, they can also break off from the original (primary) tumour and enter the bloodstream or lymphatic system. If the cancer cells are not detected by the immune system, which helps defend the body against infection and disease, they can be carried by the blood and lymph to form a new tumour in another area of the body. A tumour in a new location must develop its own blood supply (a process called angiogenesis) to survive and grow.
Because blood cells travel throughout the body, blood-related cancers like leukemia, lymphoma and multiple myeloma are usually not localized when the cancer is diagnosed. These cancer cells may be found in the blood, lymph nodes or other parts of the body, such as the liver or bones. This type of spread is not typically called a metastasis.
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Where cancer can spread
Localized cancer means the cancer is confined to the original site. Regional spread means the cancer has either grown into surrounding tissues or nearby lymph nodes. The term metastatic cancer is usually only used for cancer that has spread to distant organs or distant lymph nodes (distant metastasis).
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Common sites of metastases
Cancer can spread almost anywhere in the body. The most common sites of metastases are:
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Why cancers spread
All cancers have the potential to spread. Whether metastases will develop depends on many factors:
- the type of cancer
- Some types of cancer tend to spread to certain parts of the body.
- Breast cancer most often spreads to the bones, liver, lung or brain.
- Colorectal cancer tends to spread to the liver.
- Lung cancer often spreads to the brain, bones or liver.
- Prostate cancer tends to spread to the bones.
- the grade of the cancer
- Low-grade cancer cells are less aggressive and are less likely to metastasize.
- High-grade cancer cells are more aggressive and are more likely to metastasize.
- the length of time the cancer has been present
- The risk of metastasis increases the longer a tumour is in the body.
- the cancer cells’ ability to create a blood supply in a new location
- A cancerous tumour needs to set up a blood supply to grow.
- the location of the primary tumour
- Each type of cancer has a particular way that it spreads. Many metastases develop in the first area of blood vessels that cancer cells come to after leaving the primary tumour. After leaving the primary tumour, the lungs are one of the first places metastatic cells can be carried to by the bloodstream. This may explain why metastases form in the lungs.
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Signs and symptoms
Some people may have no or few symptoms related to their metastasis. Therefore, a metastatic cancer may only be discovered during a routine examination or test. Symptoms of metastatic cancer will depend on the particular location and size of the metastasis.
- Bone metastases may cause pain or a break in the bone (fracture).It can also put pressure on a nerve or the spinal cord, which can cause numbness or muscle weakness.
- Brain metastases may cause headaches, problems with balance or coordination, or seizures.
- Liver metastases may cause abdominal pain, abdominal swelling or jaundice.
- Lung metastases may cause cough or shortness of breath.
Getting regular checkups and reporting new symptoms are the best ways to detect metastatic cancer early.
In some cases, the metastatic tumour is found before the primary tumour because it produces symptoms before the primary tumour does.
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Diagnosis
Diagnostic tests will be done if the signs and symptoms of metastatic cancer are present, if the result of a follow-up test is abnormal or if the doctor suspects a metastasis. The types of tests done will depend on the area of the body where doctors suspect the cancer has spread. Tests may include:
- complete physical examination
- laboratory tests
- In some cases, tumour marker tests are done. Tumour markers are substances – usually proteins – that may indicate cancer is present. Tumour markers for metastatic cancer are usually measured by doing blood tests.
- imaging tests
- A bone scan is done to see if cancer has spread to the bone.
- A computed tomography (CT) scan of the head is done to see if cancer has spread to the brain.
- An ultrasound or CT scan of the abdomen may be done to see if cancer has spread to the liver.
- An x-ray or CT scan of the chest may be done to see if cancer has spread to the lung.
- In some cancers, a positron emission tomography (PET) scan can detect small amounts of cancer in different parts of the body where the cancer may have spread.
- biopsy
- To find out if a tumour is primary or metastatic, some of the cancerous tissue may be removed and examined under a microscope. This will show if the cancer cells developed in that area or if they have spread from another area of the body.
- Sometimes a metastatic tumour is found, but doctors do not know where the cancer started (primary site). This is called cancer of unknown primary.
Additional tests may be done to determine if a metastasis is present, where it is in the body and how extensive it is.
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Staging
Staging is a way of describing or classifying a cancer based on the extent of cancer in the body. When cancer has spread beyond the primary tumour location to distant organs or sites, it is said to have metastasized. Metastatic cancer can be found before or at the same time as the primary tumour. It can also develop after the primary cancer is diagnosed.
Cancer cells frequently spread to lymph nodes near the primary tumour. These are called regional lymph nodes. Cancer that spreads to lymph nodes far from the primary tumour (distant lymph nodes) is usually called metastatic disease.
Recurrence means that cancer has come back after it has been treated. Cancer can recur several weeks, months or years after treatment. If someone has been treated for cancer and doctors find a new tumour in a different location, it is usually a metastasis of the original cancer. It is possible to develop a new primary tumour unrelated to the original cancer, but this is very unusual.
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Prognosis and survival
People with metastatic cancer should talk to their doctor about their prognosis. Prognosis depends on many factors. The doctor will put the following information together with survival statistics to arrive at a prognosis for each individual:
- a person’s medical history
- type of primary cancer
- extent of metastasis
- characteristics of the cancer
- treatments chosen
- response to treatment
The doctor is the most qualified person to answer questions about what the future might hold for someone with metastatic cancer.
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Treatment
Each person with metastatic cancer will have a treatment plan designed for them by their healthcare team. The team will recommend treatment options based on the specific characteristics of the cancer and the unique needs of the person. Treatment of metastatic cancer depends on many factors, including:
- where the cancer first started (primary site)
- where the cancer has spread – the number, size and location of metastases
- the person's age and overall health
- previous treatment
Treatment for metastatic cancer is often aimed at controlling symptoms and slowing the progression of the cancer.
A treatment plan for metastatic cancer may include one or more of the following:
The person with metastatic cancer will have regular follow-up visits to check how they respond to treatment or to see how well their symptoms are being controlled.
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Supportive care
A cancer diagnosis can lead to many challenges for people with cancer and their families. Each person's experience will be different because their cancer, treatment and recovery are different. A person with metastatic cancer may have concerns about:
- pain
- symptoms of advanced cancer
- the future
There are many treatments and strategies that can help people with metastatic cancer manage their symptoms and improve their quality of life.
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Clinical trials
Canada is an international leader in conducting research studies called clinical trials. A person with metastatic cancer may be offered the opportunity to participate in a clinical trial. Clinical trials for metastatic cancer are often included in studies being done for a particular type of primary cancer. The primary type of cancer is often the best place to first look for metastatic cancer clinical trials. However, there may also be trials that study certain types of metastatic cancer.
For more information, go to clinical trials.
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