What is metastasis?
Metastasis is a word used to describe the spread of cancer. Unlike normal cells, cancer cells have the ability to grow outside of the place in the body where they originated. When this happens, it is called metastatic cancer. Nearly all types of cancer have the ability to metastasize, but whether they do depends on a variety of individual factors. Metastases can occur in three ways:
- They can grow directly into the tissue surrounding the tumor;
- Cells can travel through the bloodstream to distant locations; or
- Cells can travel through the lymph system to nearby or distant lymph nodes.
Common sites of metastasis
Sometimes, a metastasis will be found without a known primary cancer.
In this situation, an extensive search is done to look for the primary cancer source. If none can be found, it is considered a case of cancer of unknown primary (CUPS).
Some people will have no or minimal symptoms of metastatic cancer. If there are cancer symptoms, they are based on the location of the metastasis.
Bone metastasis may or may not cause pain. Occasionally, the first sign of bone metastasis is when a bone breaks with a minor injury or no injury. *Severe back pain accompanied by leg numbness or difficulty with bowel or bladder control, must be evaluated by a doctor immediately.
Cancer symptoms of lung metastasis are usually very vague and can be related to other problems that are unrelated to the cancer. They can include a cough (productive or nonproductive), coughing up blood, chest pain or shortness of breath.
Liver metastasis can cause pain, weight loss, nausea, loss of appetite, abdominal fluid (ascites) or jaundice (yellowing of the skin and the whites of eyes, dark urine, light colored stools).
There is no one test to check for metastasis. Various tests will reveal different things. The tests that are done are determined by the type of primary cancer and/or any symptoms that need to be investigated.
Routine blood tests such as liver enzymes may be elevated in the presence of liver metastasis. However, these blood tests are often normal, even in people with advanced disease.
Some cancers have specific blood tests that can be helpful in following the disease AFTER it has been diagnosed. If these levels rise, it can be an indication that the disease is active or progressing. Some examples are:
- Colon cancer: CEA (carcinoembryonic antigen)
- Ovarian cancer: CA-125
- Prostate cancer: PSA (prostate specific antigen)
- Testes cancer: AFP (alpha-feto-protein)
- HCG (human chorionic gonadotropin)
There are several tumor markers that are less specific, and therefore, not used as a tool for diagnosing metastasis.
There are many tests that are designed to “take pictures” of various parts of the insides of the body. The type of tests done will depend on the symptoms and/or the type of cancer.
Ultrasound is one way to evaluate the abdomen if a mass is suspected. It is a good tool for identifying fluid in the abdomen and it is good at distinguishing fluid-filled liver cysts from more solid, suspicious-appearing masses within the liver or the pelvis.
CT scan (computed tomography) can be used to scan the head, neck, chest, abdomen and pelvis. When done with contrast, it is especially good at identifying masses within the lymph nodes, lungs, liver or other structures.
Bone scan is done with a radioactive tracer that attaches to damaged bones and shows as a “hot spot” on the scan. It is most useful at evaluating the whole body for evidence of bone damage that is suspicious for cancer. If there is concern for a bone breaking, additional plain X-rays may be done to further define the extent of damage.
MRI (magnetic resonance imaging) is a test using radio waves and magnets to create an image. MRI is best used to define potential damage to the spinal cord if there are bone metastasis in the vertebra of the back or to characterize brain metastases.
PET scan (positron emission tomography) works to identify areas of hypermetabolic activity anywhere in the body. A radioactive substance is given to the patient and this attaches to glucose, which is attracted to cells that are hypermetabolic. When the scan is done, these areas "light up." Often, but not always, cancer cells fall into this category of being hypermetabolic. In addition, not everything that is hypermetabolic is cancer.
The results of these and other tests may not provide definitive information. The findings must be correlated with each other, the physical examination, symptoms, and in some cases biopsy.
Metastasis is primarily treated based on the original site of the cancer. For example, if a person has breast cancer and cancer spreads to the liver, it is still treated with the same drugs used for breast cancer – because the cancer cells themselves have not changed, they are just living in a new place.
In some clinical situations, metastases may be treated in specific ways.
Depending on the number of tumors and the extent of the disease in the rest of the body, treatment options may include surgery (in very specific cases), radiation therapy, gamma knife surgery, chemotherapy and/or steroids.
If the bone metastases are not causing pain or danger of breaking, they may be monitored or treated with drug therapy. If there is pain or the bone is fragile, radiation may be given to the location of the damage.
The treatment of lung metastases depends on the extent of the metastases as well as the primary cancer. In most cases, it will be treated in the same manner (with the same drugs) as the primary cancer. If the metastasis is causing fluid to form around the lung, a procedure (thoracentesis) may be done to remove the fluid to make breathing easier.
There are a variety of ways to treat liver metastases depending on the type and extent of the primary cancer as well as the number and size of the liver metastases. In many cases, liver metastases will be treated in the same manner (with the same drugs) as the primary cancer.
In instances where there is limited disease, both primary and metastatic, there are several novel approaches including surgery and radiofrequency ablation (RFA), for example. Organ transplant is generally NOT an option for metastatic disease.