Lung Cancer Metastasis
Metastasis is a process where cancer cells spread from their initial location, known as the primary tumor, to form a tumor in another part of the body. If the cancer cells spread from the primary tumor to form one or more secondary tumors, they take the name of their primary source. For instance, if cancer forms in the lungs and spreads to the liver, the new tumor is called metastatic lung cancer, not liver cancer.
In all cancers, metastasis is a primary danger that directly impacts the patient's life expectancy. For example, lung cancer patients usually die from metastatic tumor complications, not from damage the primary cancer does to the lung itself. Also, the extent of metastasis strongly influences the cancer's staging and treatment. The staging system for lung cancer and most effective treatment options differ greatly depending on how the cancer cells are classified — as either small cell lung cancer (SCLC) or non-small cell lung cancer (NSCLC).
Primary lung cancers typically metastasize to the adrenal glands, liver, bones and brain. Though cigarette smoking is the leading cause of lung cancer, the disease can also occur after exposure to asbestos, industrial chemicals and radon gas. If you have been diagnosed with an asbestos-related lung condition, set an appointment with a specialist by using the free Doctor Match program.
Virtually all cancers can form metastatic tumors, but the speed, aggressiveness and destination of the spreading varies greatly by cancer type. Highly metastatic cancers will spread to other organs quickly while other cancers spread over the course of years or decades.
How Does Cancer Spread?
Unlike healthy cells, cancer cells do not stick together well and often detach from tumors. Local spread can occur when cells break away from a primary tumor and invade nearby tissues. To reach distant locations, cancer cells must enter one of the two main pathways for metastasis: the bloodstream or the lymphatic system.
Through the Bloodstream
To enter the bloodstream, a tumor's cancer cells detach and pass through the walls of blood vessels. The venous system, which is responsible for returning blood to the heart, is a complex system of veins that easily promotes metastasis. All cancers are likely to spread to the liver and lungs because the venous system passes a high volume of blood through these organs. Once in the bloodstream, a cancer cell circulates throughout the body until it becomes stuck. This typically occurs in capillaries, the smallest type of blood vessel. Cancer cells can then break through capillary walls and invade nearby tissue or organs and begin to multiply.
Through the Lymphatic System
Cancer cells enter the lymphatic system through the same process they enter the bloodstream. Like the bloodstream, the lymphatic system is widespread throughout the body and has several important circulatory functions. It also promotes metastasis because of its close proximity to many of the body's tissues. Once a cancer circulates through the lymph fluid, it can become stuck in the narrow channels of the lymph nodes and form secondary tumors. It is common for cancer cells to become trapped in lymph nodes close to the primary tumor.
The Role of Angiogenesis in Metastasis
Even with the great circulation abilities of the blood and lymphatic system, lung cancer metastasis is not possible without a process called angiogenesis. Tumors will not grow beyond a tiny size without an adequate supply of oxygen and nutrients provided by fresh blood. By triggering angiogenesis, a cancer cell creates new blood vessels that sustain secondary tumor growth. Doctors are currently testing several anti-angiogenesis drugs that aim to prevent this process, thereby halting a tumor's ability to metastasize and grow.
Metastatic Lung Cancer
Lung cancer's ability to spread depends on several key factors. The individual properties of the cancer cells are important, as are the properties of the cell at its final destination and any cells it encounters along the way. All of these factors are significant since not all cancer cells have the ability to spread, and immune system cells can sometimes block metastasis. Even if cells of the immune system fail and cancer reaches another location in the body, a metastatic tumor will not form unless the site can support its growth.
Each of the many specific lung cancer types has the ability to spread, but the aggressiveness, location and patient outlook will vary based on the cancer's classification. Doctors typically classify all lung cancers as either small cell lung cancer (SCLC) or non-small cell lung cancer (NSCLC). Lung cancers are grouped this way based on similarities in treatment practices and likely survival rates, though within these groups subtypes will grow and spread in distinct ways.
Non-Small Cell Lung Cancer
Approximately 85 to 90 percent of all lung cancers are of the non-small cell variety. Fortunately, these cancers grow and spread at a much slower rate than their small cell counterparts. This quality makes surgery an effective treatment option for non-small cell lung cancer if the cancer is detected early on, although non-small cell lung cancer usually causes few or no symptoms until the cancer is in its later and less manageable stages.
The progress of non-small cell lung cancers is described according to the TNM staging system, which classifies the cancer in terms of tumor size (T), lymph node involvement (N), and extent of metastasis (M). This type of cancer most frequently spreads to the lymph nodes, followed by the lining of the lungs (pleura), liver, bone and brain.
Small Cell Lung Cancer
Small cell lung cancers are highly aggressive and tend to rapidly spread to the lymph nodes and distant organs. Metastasis often occurs before the patient experiences any symptoms, which combined with its aggressiveness makes small cell lung cancer an especially fatal disease with a short life expectancy.
Doctors prefer a two-stage classification system for small cell lung cancer. In the limited stage, the cancer is confined to one lung and possibly lymph nodes on the affected side of the chest. If the cancer is detected at this stage, tumors can often be surgically removed, which greatly increases the patient's outlook. However, nearly 67 percent of small cell lung cancer patients are diagnosed with extensive-stage cancer, which means metastasis has formed secondary tumors somewhere in the body. Once the cancer has spread, surgery is rarely recommended or even an option.
When Cancer Spreads to the Lungs
After invading the bloodstream or lymphatic system, cancer that forms in any part of the body can easily metastasize to the lungs. This is because the blood and lymph flow passes through the lungs and the organ has one of the body's densest capillary networks. Between 20 and 54 percent of all cancers will spread to the lungs, which receive more secondary tumors than any other organ.
The cancers that most commonly metastasize to the lungs include breast, colon, stomach, pancreas and kidney cancer. It is important to understand that a cancer that spreads to the lungs is not actually lung cancer. Cancer that invades the lungs is a completely different disease than cancer that forms in the lungs, and effective treatment options will vary significantly.
Treating Metastatic Lung Cancer
When metastasis occurs and lung cancer spreads to another organ, treatment becomes increasingly difficult. Surgically removing a tumor and nearby tissue is a highly effective treatment for lung cancer. But if the cancer has spread, surgery can be risky and time consuming.
Lung cancer metastases are often treated with radiation therapy, but usually to relieve symptoms and pain rather than actually cure the cancer. Chemotherapy tends to be a more successful treatment option since it kills cancer cells, limits further metastasis and often improves a patient's quality of life and overall outlook. Though it doesn't completely kill the cancer in most cases, two cycles of chemotherapy will show a response or decrease in tumor size 65 to 70 percent of the time.
Huge efforts in cancer research aim to prevent metastasis. Drugs like Avastin limit the spread of cancer by halting the process of angiogenesis. By blocking the growth of new blood vessels, anti-angiogenic drugs cut off the nutrients a tumor needs to sustain itself or spread.
Hundreds of clinical trials are currently underway to help doctors and researchers find the most effective combinations and dosages of anti-angiogenic drugs for lung cancer and other asbestos-related cancers, such as mesothelioma. Speak to a Patient Advocate to find out if you qualify for participation in one of these clinical trials. Call (800) 615-2270 to learn more.
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Last Modified Thursday, May 17th, 2012 | Disclaimer | Privacy Policy |
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