Metastasis is the spread of cancer cells from the original site to other parts of the body.
As cancer grows and changes, cells lose their ability to stay in a single tumor mass. When cancer cells get into the lymph system or blood vessels, 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 almost 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 and take hold in certain locations. Common sites are the brain, lungs, liver, lymph nodes, bone, skin, and adrenal glands.
Some cancers already involve much of the body when they are first detected. This is common with cancers such as leukemia and lymphoma. Where and when a cancer will spread depends on many factors. These factors include the primary tissue type and the genetic abnormality of the cancer.
The particular genetic changes in the cancer may make it more prone to spread. Metastasis in part depends on how different the cancer is from surrounding tissue, whether certain genes are activated, and how close the cancer is to lymph nodes 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 tumors and basal cell or squamous cell carcinoma of the skin.
The symptoms of metastasis depend on the site of spread. In metastasis to the brain and central nervous system, symptoms include the following:
The following symptoms can be caused by tumors in the lungs:
Liver metastasis can cause an enlarged painful liver, loss of appetite, and jaundice, or yellowing of the skin.
Other common problems are as follows:
If cancer cells metastasize to the bone marrow, they may interfere with production of blood cells. The individual may have the following problems:
Less commonly, a metastasis may cause the adrenal gland to fail. The kidney or gallbladder ducts may become blocked. Many other symptoms are possible. These symptoms are not necessarily linked to a certain kind of cancer.
The diagnosis of metastasis begins with a medical history and physical exam. The healthcare provider may order various blood tests, including those for tumor markers. X-rays and other imaging studies are often used to diagnose a metastasis. Special X-rays, such as MRIs and CT scans, may be used. These can sometimes find tumors smaller than 1/2 centimeter. 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 tumors. 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 tumor, or examination of a bone marrow sample.
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 therapy are used as treatment. The prevention and control of metastases is an active area of cancer research.
Some cancers with metastasis can be cured. These include tumors that are highly sensitive to radiation therapy or chemotherapy. Following are some examples:
People can live with metastases for many years. These cancers may include:
Metastasis usually leads to death if it cannot be removed or treated.
Metastases are not contagious. They pose no risk to others.
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 therapy can be useful for local tumor recurrence. Otherwise, systemic therapy is needed. This includes chemotherapy and biological response modifiers. These treatments are administered intravenously or orally. They treat malignant cells wherever they are.
Much research is being done on treating metastases. Other approaches are being tried. These include anticoagulation of the blood, enzyme inhibitors, gene therapy, and growth factor inhibitors. Such treatments are experimental.
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, and allergic reaction to anesthesia.
Radiation therapy 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 biological response modifiers have many side effects, depending on the medicines used. Side effects can be mild, such as nausea, temporary hair loss, and fatigue. More severe nausea and fatigue can be treated with new medicines. Side effects can also be life-threatening, such as severe infections, secondary tumors, severe blood clots, or organ damage.
Some metastases are curable, while others are not. Some treatments have late complications.
The person is watched for any recurrence of metastases. Physical exams, blood tests, and tests for tumor markers are done. Chest X-rays, CT 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. Any new or worsening symptoms should be reported to the healthcare provider.
Author:Thomas Fisher, MD
Editor:Ballenberg, Sally, BS
Reviewer:Adam Brochert, MD