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Metastatic cancer refers to any form of cancer that has spread from its original point of development to other parts of the body. Cancers can spread through the lymph nodes or through the blood stream, and the same is true for mesothelioma.
Doctors know that some cancers are predictable as far as the organs to which they will metastasize. In some instances, this predictability can guide doctors and help keep an eye on certain parts of the body that are susceptible to tumors.
Because mesothelioma is not generally diagnosed until its later stages (usually stage III or stage IV), metastatic disease is common at the time of diagnosis. Mesothelioma metastasis, however, can also occur as the disease continues to progress.
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Mesothelioma is known as a particularly aggressive cancer with a range of development rates. Although the genetic changes that lead to the disease's initial development can take decades, the cancer grows quickly and spreads to other parts of the body within a matter of months. What makes it so aggressive, and how does this affect life expectancy?
The cancer's aggression is partly a result of its location. It almost always develops in the chest cavity or the abdominal cavity, where it readily affects vital organs like the lungs and heart.
Certain types of tumor cells are also particularly dangerous and can spread more efficiently. These factors can lead to short survival times of a year or less, but proper treatment can help prolong life.
Unlike many other cancers, mesothelioma progression does not generally impact the bones or brain, but normally affects the organs around the lungs on the side of the body in which the original tumor was found. This is known in the medical field as a "local spread."
It is also theorized that mesothelioma may actually travel more quickly than other types of cancer. This is because the disease is most often located in or near the lungs, which transfer oxygen throughout the body. Therefore, cancer cells may be able to enter the bloodstream and circulate through the body.
Cancer progression can sometimes be detected through diagnostic imaging tests, which include MRIs or CT scans. Doctors usually suspect that a cancer has spread when a patient complains of symptoms that are not generally associated with asbestos cancer. At that time, tests or biopsies will be performed.
Angiogenesis is the process of new blood vessels forming in a body, and it how cancerous tumors spread. Without angiogenesis, tumors cannot spread from a point of origin to other parts of the body.
In layman's terms, new blood vessels form when cancerous cells release molecules that reach nearby normal tissue. This process activates genes that make proteins, which encourage new blood vessel growth.
Some researchers believe the complex angiogenesis process may be a key to slowing or halting the spread of cancer. They are studying what promotes and inhibits angiogenesis. In addition, a number of anti-angiogenic medications that are in clinical development.
Drugs being evaluated for mesothelioma metastasis include semaxanib (SU5416), thalidomide and tetrathiomolybdate. In clinical trials, the three medications demonstrate an ability to help stabilize the disease and increase survival.
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Stages of Cancer Development
Doctors use a staging system to help gauge the development of pleural cancer. The disease is the least developed at stage I, when the cancer is localized to its origin site. At this stage, the cancer may be treated with potentially curative measures such as surgery, chemotherapy and/or radiation therapy.
Patients diagnosed at stage I have the best prognosis, living a median of two to three years.
By stage IV, the cancer has metastasized, and tumors have developed in distant areas of the body. This is the most difficult to treat because the cancer is so widespread. At this stage of development, treatment is limited to palliative, symptom-controlling care. This leads to a life expectancy of less than a year.
Tumor Location Affects Development
The site of the cancer affects how quickly it initially develops, as well as how fast it spreads.
Mesothelioma can develop in one of four areas of the body:
Overall, mesothelioma has a latency period of 20 to 50 years, meaning it can take two to five decades for damaged cells to become cancerous. But this latency period varies slightly based on where the cancer develops. Pleural is the most common type and has a typical latency period of 30 to 50 years. The next most frequent type, peritoneal, only takes about 20 to 30 years to appear.
After initial tumor growth, location can help predict further development rates. Pericardial cancer is considered the most aggressive. The tumor grows in such close proximity to the heart and causes immediate complications, leading to a mean survival time of five to eight months after diagnosis. Other types develop almost as quickly.
Cell Type Affects Development
In addition to location and histological type of tumor, life expectancy may be affected by patient factors such as age and overall health, as well as available treatment options in each specific case. Life span is also affected by the cancer's stage of development.
Once the cancer manifests, it continues to develop by growing larger and spreading to other areas of the body, a process called metastasis. The rate of metastasis depends in part on the cellular makeup of the tumor. Tumors with an epithelial makeup have a uniform, ordered structure and must spread via lymph nodes. These tumors are typically less aggressive and spread more slowly, adding time to life expectancy.
Sarcomatoid and biphasic mesothelioma, on the other hand, are more randomized and complex. These types of cells can spread through the blood, a speedier process than lymph node involvement. So, these tumors spread to other areas of the body more quickly, minimizing treatment options and reducing expected life span.
Some studies indicate that pleural mesothelioma plays a role in the spreading of cancer to areas of the body where the disease is not often found. One of those areas is in or near the brain.
Although not as common as localized metastases, mesothelioma brain metastases have been reported in medical literature. Malignant mesothelioma does not typically spread to the brain, bones or adrenal glands, so patients should not be highly concerned about brain metastases.
However, there are cases where cancer spreads from the lung lining to the brain. A case report from Wisconsin in 2003 concluded that specialists should consider the central nervous system "as a possible site for distant spread of malignant mesothelioma." That was reached after a 65-year-old patient with pleural cancer was also found to have a cancer mass in his brain.
An earlier case report, that of a 58-year-old Japanese woman in 1989, revealed that her pleural cancer did not respond to traditional treatment, including chemotherapy. After her chemotherapy was halted, she developed a mass behind her right eye. X-rays showed the mass in addition to increased size of her pleural tumor.
In the cases that have been reported, the mesothelioma diagnosis was typically given in a late stage of development. Once the cancer has spread to distant parts of the body, treatment options tend to be palliative in nature (which aims to relieve symptoms and provide comfort rather than cure the disease).
Bone metastases in cancer patients can cause a variety of problems, and they are also difficult to detect. Few mesothelioma patients are shown to have metastases in their bones. In fact, there is no agreement in the medical community about how often mesothelioma patients develop this condition.
Patients who do develop it suffer bone pain, fractures or spinal cord compression. Doctors test for the spread of cancer to the bones with a bone marrow biopsy or a bone marrow aspiration.
If mesothelioma bone metastasis is suspected in a patient, doctors can run a number of tests to form an accurate diagnosis. Testing starts with a blood or urine sample, which may show abnormalities. For example, a high level of calcium in a blood sample may indicate this condition.
Little is known about its effects on prognosis, but a timely diagnosis and proper treatment can help extend life span.
Once mesothelioma has metastasized, treatment of the disease will probably change from its original course. The oncologist will need to address the cancer that has spread to other parts of the body and may recommend different therapies. In some cases, both chemotherapy for mesothelioma and radiation may be suggested. However, once the cancer has spread, doctors can usually only offer palliative treatments to ease the pain and improve the quality of life for the patient.
An oncologist with experience in treating this aggressive asbestos-related disease will be able to recommend the best course of treatment for both the original disease and the metastases.