Metastasis is a term that describes how far a disease has spread in the body. It is applied to most forms of cancer. Mesothelioma is a type of cancer that can and often does metastasize from its primary tumor. In fact, very few cases of benign mesothelioma tumors have been recorded.
One of the major issues with mesothelioma is that it rarely gets diagnosed in its earlier stages. During late-stage mesothelioma (stage 3 or 4), the disease begins to metastasize and affect other organs and tissues. This obviously does not make for good prognoses. In fact, the life expectancy for stage 4 mesothelioma is generally less than a year.
Mesothelioma also has a reputation as a very aggressive disease, often metastasizing much quicker than other types of cancer. That being said, mesothelioma takes a long time to start inducing symptoms in patients.
Exposure to asbestos causes mesothelioma, but it can take many decades (usually between 30 and 40 years) for the disease to start showing any symptoms. In early stage mesothelioma, symptoms may not be present or noticeable at all.
How Mesothelioma Metastasis Works
As noted above, the spread of mesothelioma is rather quick compared to other, similar types of cancer. There are several avenues the disease takes to further its spread, as well. The most obvious is that cancerous cells simply make their way from the primary tumor to other nearby organs and tissues and begin spreading out from there.
For example, the most common type of the disease is pleural mesothelioma which occurs in the lining of the lungs (or pleura). As the primary tumor begins to grow in the pleura, its cancerous cells will start to make their way onto the chest wall or into one of the lungs. Once they’ve reached these new areas, the cells continue to multiply and grow, often creating secondary tumors that produce further metastasis.
Other methods for mesothelioma metastasis include:
- Traveling through the bloodstream or lymphatic system
- Using blood vessels or lymph nodes near the original tumor
- Creating new blood vessels (angiogenesis)
These metastasis methods account for the widespread of mesothelioma throughout the body. With angiogenesis, the cancer cells can create new blood vessels to grow more tumors at a much faster rate. Travel through the lymphatic system or bloodstream means that the cells can effectively attack any tissue or organ.
Staging and Mesothelioma Metastasis
The American Joint Committee on Cancer (AJCC) developed the only clinically-accepted staging system for mesothelioma known as the TNM method. TNM stands for tumor, node, and metastasis which are all categories that are used to classify the disease’s spread. There are 4 stages, with stage 1 having the best outlook and stage 4 having the worst.
Using the AJCC’s method, metastasis can only occur in stages 3 and 4 of the disease. While minor spreading can happen in stages 1 and 2, it is usually confined to a small area of the body. In general, secondary tumors begin forming in stage 3 of the disease. Also in stage 3, organs and lymph nodes on the same side of the body as the primary tumor are affected.
Stage 4 is characterized by mesothelioma spread to multiple organs and tissues on both sides of the body. For instance, stage 3 pleura mesothelioma might affect one lung on the same side of the body as the primary tumor whereas stage 4 pleural mesothelioma would likely affect both lungs. Lymph nodes are also affected in stage 4.
Where Does Mesothelioma Metastasis Occur?
As a general rule, metastasis can occur virtually anywhere throughout the body. It will start out in the region of the body where the primary tumor is located. There are three main types of mesothelioma where tumors start to form.
- Pleural mesothelioma (located in the lining of the lung)
- Peritoneal mesothelioma (located in the lining of the abdominal cavity)
- Pericardial mesothelioma (located in the lining of the heart)
All of these types of this disease will metastasize if left unchecked. The pleural form will start in the chest cavity, the peritoneal form will start in the abdominal cavity, and the pericardial form will begin in the mediastinum (a structure in the thoracic cavity).
As the disease progresses, a variety of major organs and tissues may be invaded, including:
- Adrenal glands
All three types of the disease can metastasize to these organs, and, in general, these organs are the most susceptible after the primary tumor begins spreading. Again, any organ and tissue in the body can be affected by the spread of mesothelioma. In fact, in rare cases, mesothelioma metastasis has attacked the bones or the brain.
But how does each separate form of the disease individually spread?
Pleural Mesothelioma Metastasis
Pleural mesothelioma is the most common type of the disease making up around 70 to 90% of all diagnoses. Because of this, it is the most well-known and well-understood type of this disease. In fact, the TNM staging system has only been clinically-approved for use with the pleural form of the disease.
As noted above, pleural mesothelioma begins with cancerous cells and a tumor in the lining of the lungs or pleura. Some minor local spreading may occur by stage 2, but full metastasis is only considered to have happened at stage 3.
Other characteristics of stage 3 mesothelioma include:
- Spread to the lymph nodes on the same side as the original tumor
- Spread to diaphragm
- Spread to esophagus
- Spread to the lining of the heart (pericardium)
The diaphragm, esophagus, and heart lining are all a part of the thoracic cavity and are therefore more likely to be hit by pleural mesothelioma metastasis. The precise organs or tissues that are affected are often different for each patient. For instance, in one case, the disease could have spread to the esophagus while another case shows no spread to that area.
By stage 4, the tumors will usually be much larger, and the spread of the disease will have affected most of the thoracic cavity. Distant organs like the spleen, liver, kidneys, or the lung on the opposite side of the tumor may also be affected. Lymph nodes on both sides of the body also see metastasis. In rare cases, bone and brain metastasis can occur.
Peritoneal Mesothelioma Metastasis
Peritoneal mesothelioma occurs in about 10 to 20% of cases and affects the lining of the abdominal cavity. Cancer cells and a tumor usually begin to form there. Unlike pleural mesothelioma, there is no clinically-accepted staging system that is approved for use in diagnosing peritoneal mesothelioma. Doctors may follow general guidelines or will use the Peritoneal Cancer Index (PCI) which stages the disease based on the size of tumors in the abdomen.
It is generally accepted that metastasis does not occur until stage 3 of the disease. During this stage, lymph node involvement is possible, and the cancerous cells and possibly secondary tumors have spread to other abdominal organs like the stomach or liver.
By stage 4, the spread is even more dramatic with tumors and cancer cells possibly attacking any of the following:
- Blood vessels
- Adrenal glands
- Pleural cavity
Like with pleural mesothelioma, metastasis can occur in the brain and bones, but it is even rarer with the peritoneal variety.
Pericardial Mesothelioma Metastasis
Very little is known about pericardial mesothelioma because it is very rare, occurring in about 1% of all cases. It is not uncommon for pericardial mesothelioma to be diagnosed only after the patient has passed.
This form of the disease metastasizes very quickly, partially because the cancerous cells end up in the heart and the pulmonary artery. Secondary tumors have been found in the chest and abdominal cavities as well as in the lungs and lymphatic system.
Cell Type and Metastasis
Mesothelioma can also be further differentiated by its cell type. The cell type often determines how the disease forms and spreads long-term.
There are three main mesothelioma cell types:
Epithelioid cells are the most common and occur most frequently in pleural mesothelioma. They are also the least aggressive when it comes to metastasis. The cells divide very rapidly, and they do so in clusters; this means that metastasis is slower.
Sarcomatoid mesothelioma, on the other hand, has the most aggressive metastasis. Sarcomatoid cells most frequently appear in peritoneal mesothelioma and can reduce life expectancies greatly.
Biphasic cells are a combination of both epithelioid and sarcomatoid cells. These cells most often appear in peritoneal mesothelioma, as well.
The amount of metastasis with biphasic cells depends on whether epithelioid cells or sarcomatoid cells are dominant.
Metastatic Mesothelioma Symptoms
Most symptoms of mesothelioma again depend on the location of the disease. As the disease metastasizes, many symptoms start to overlap. Difficulty breathing, chest and abdominal pain, difficulty swallowing, excess fluid buildup in the chest or abdomen, and numerous other symptoms can start to show up as the disease progresses.
Many patients only start to notice their symptoms when the disease reaches stage 3 and sometimes stage 4. So, metastasis has already set in. As tumors grow, they may also put pressure on other organs without metastasizing to them.
Very late stage mesothelioma often includes damage to the nervous system to some degree. Many patients experience Horner’s syndrome, a nerve condition that inhibits the ability of the eyes, and laryngeal nerve palsy, a nerve condition that involves the paralysis of the voice box.
The latter condition can also make it difficult for patients to speak.
Treatment Options for Late-Stage Mesothelioma
The spread of mesothelioma is pernicious and often silent in the early stages. After metastasis has begun, the prognosis for most patients is not very positive. Unfortunately, most patients will be diagnosed after metastasis has started to occur. Still, treatment options may be available for certain patients.
In most cases, physicians will opt for a combination of surgery, chemotherapy, and radiation therapy. Surgical interventions often include the removal of all or part of an organ or tissue such as a lung or the lining of the abdominal cavity. This is the most efficient way to stop the spread of the disease because it literally removes the primary tumor.
Unfortunately, this option is usually reserved for patients whose mesothelioma has not metastasized. The removal of a lung may get rid of the primary tumor, but if mesothelioma metastasis has occurred, the disease is already in numerous other parts of the body. Even so, curative surgery is not out of the question even for patients with stage 4 mesothelioma.
In most cases, however, treatments for late-stage mesothelioma are palliative in nature. This means that they are only performed to improve the comfort and quality of life of the patient. Strong painkillers are typically prescribed along with anti-anxiety drugs to soothe the patient’s mind.
In some cases, surgery, chemotherapy, and radiation therapy can be palliative. For example, the surgical removal of a tumor can reduce pressure and pain in certain areas of the body. Likewise, the draining of fluid buildup can help improve breathing and reduce pain as well. A chemotherapy and radiation therapy regimen may be administered to help shrink tumors that are causing physical discomfort.
The importance of early detection for mesothelioma cannot be overstated. If the disease is caught early on, the prognosis is much better, and patients will respond better to aggressive treatments.
It’s not uncommon for patients to live several years after diagnosis of stage 1 mesothelioma.
Unfortunately, it is very uncommon for anyone to outlast their estimated life expectancy when given a stage 3 or stage 4 diagnosis. Metastasis makes it very difficult for treatment options to be effective in a curative sense. After metastasis begins, the life expectancy for those patients is usually less than 15 months.
If you start feeling early symptoms of mesothelioma like a persistent cough or chest pain, it’s important to tell your doctor about any exposure to asbestos you may have had. If you have had any exposure to asbestos in your past, then you are at risk of developing mesothelioma.
As research continues, there will be more and more treatment options available for patients, but, as it stands, catching the disease before metastasis is the best way to fight it.