Mesothelioma Metastasis

Mesothelioma metastasis occurs when the cancer has spread beyond where the tumors originated, generally associated with stage 3 and stage 4 mesothelioma. When mesothelioma metastasizes, prognosis worsens and treatment options may be limited to palliative care.

Mesothelioma is an aggressive cancer, with most patients surviving less than two years after diagnosis. The difficulties in diagnosing the disease early, largely due to the long latency period and nonspecific symptoms, means the majority of patients aren’t properly diagnosed until the cancer has progressed to a more advanced stage. By this point, the cancer has often metastasized, or spread, to other parts of the body and is much more difficult to treat. At this stage, life expectancy is typically only 12 – 16 months.

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How Does Mesothelioma Metastasize?

Mesothelioma cancer can spread through the body a number of ways, much like other types of cancer spread in the body at more advanced stages. The spreading of mesothelioma cells can be considered localized, regional or distant, depending on which tissues or organs the cancer cells can be found.

Mesothelioma, along with other types of cancer, can metastasize by:

• Cancerous cells invading nearby healthy tissue
• Traveling through nearby blood vessels or lymph nodes
• Moving through the bloodstream or lymphatic system to more distant organs
• Causing new blood vessels to grow (angiogenesis), allowing the cancer cells to grow and develop more tumors

The cancerous cells could potentially spread anywhere, though metastatic mesothelioma is often associated with spreading to certain areas of the body depending on the origin of the tumors (pleural, peritoneal or pericardial).

Mesothelioma Metastasis by Type

The type of mesothelioma you’re diagnosed with is one of the most important factors in determining how the disease will progress. Depending on the type, the disease is more likely to develop secondary tumors in particular organs or tissues based on where in the body the tumors originated.

Pleural Mesothelioma Metastasis

Malignant pleural mesothelioma, which first develops in the linings of the lungs, is the only type of mesothelioma that can be more easily defined by specific staging systems. According to one of the most used staging systems, the Tumor Node Metastasis (TNM) System, metastasis is largely consistent when the disease has advanced to stage 3 or stage 4, though patients may seem some local spreading even by stage 2.

While the metastasis to these nearby and distant organs and tissues is rather commonly associated with these stages of the cancer, doctors have also seen pleural mesothelioma spread into other specific organs. One particular clinical study gathered data for 165 malignant pleural mesothelioma patients from 1992 to 2016. Researchers were able to analyze some of these common local and distant metastases.

The local metastases largely included conditions of the lung, like pleural effusions or spreading to the other lung. On a more local level, researchers also noted spreading through the chest wall, with about 30% even affecting the lining of the heart (pericardium).

The study also noted common distant spreading, including:

• The visceral nervous system
• Liver
• Adrenal glands
• Kidneys
• Spleen

Though considered more rare events overall, the researchers also noted that 20% of the patients experienced bone metastases. Symptomatic brain metastases were also recorded in just 3% of patients. While these are certainly less common areas of the body impacted by mesothelioma progression, it’s important for patients to be aware of the possibility and keep in mind any correlating symptoms.

Peritoneal Mesothelioma Metastasis

The second most common type of mesothelioma develops in the linings of the abdomen. Peritoneal mesothelioma does not have a specific staging system, though doctors often are still able to refer to more general cancer stages to define the disease. Some also rely on the Peritoneal Cancer Index (PCI) to essentially grade the size of the tumors based on different regions of the abdomen. Like with pleural mesothelioma, metastasis is generally associated with stage 3 and stage 4 of the disease, but there still may be some localized spreading by stage 2.

While researchers have found that metastasis of peritoneal mesothelioma generally still largely affects the abdomen and more regional organs, there have been cases where the cancer has spread more widely through the body. Peritoneal mesothelioma metastasis isn’t as well understood or documented as pleural mesothelioma, as there are only about 500 new cases each year.

Some common areas of the body that develop secondary tumors from peritoneal mesothelioma include:

• Adrenal glands
• Liver
• Spleen
• Kidneys
• Diaphragm

Researchers have also found instances of peritoneal mesothelioma metastasizing to the bones and brain, though this is even rarer than with pleural mesothelioma. Secondary tumors are most common in nearby organs, as well as occasionally developing in the pericardium or pleural cavities.

Pericardial Mesothelioma Metastasis

Unfortunately, not much is known about pericardial mesothelioma in general because it is so rare. For the majority of patients facing this diagnosis, it is not properly detected until posthumously. However, there are some noted reports around the disease and how it may further develop in the body as it gets to later stages.

The primary tumors for pericardial mesothelioma develop in the lining of the heart, pericardium. Sometimes pericardial mesothelioma tumors may be secondary from other types of the disease or other cancers.

In some studies, researchers have found the cancer spread to various organs and tissues including:

• Liver
• Chest wall
• Abdominal cavity
• Lungs
• Lymphatic system

In studies of pericardial mesothelioma, researchers have largely noted how the cancer spreads through the heart and the pulmonary artery, which can ultimately help spread the cancer to other systems and organs.

Other Factors Impacting Metastasis

In addition to the type of cancer, there are other signals that can greatly impact how the mesothelioma will likely spread and develop in the body. Considering all of these elements of one’s diagnosis will have a large impact on a patient’s life expectancy.

Stage at Diagnosis

Though it seems obvious, stage of the disease at the time of the mesothelioma diagnosis is one of the most important factors that will indicate if and how the cancer has spread, as well as how it may progress over time. If the disease can be diagnosed at an early stage, patients will see no or minimal metastasis and have a much better survival time.

Cell Type

In addition to where the tumors originate in the body, the mesothelioma cell type associated with these tumors has a big influence on how the cancer may spread. Epithelioid cells, for instance, can grow and divide quickly, but typically metastasize slowly because the cells stay together in groups. Patients diagnosed with sarcomatoid mesothelioma, however, face the worst prognosis because these cells have a particularly aggressive growth rate and tend to spread quickly. Biphasic mesothelioma can have a more varied impact on metastasis, depending on if sarcomatoid cells or epithelioid cells are more dominant.

Response to Treatment

With all these other factors in mind, how a patient’s cancer responds to treatment may also influence if the cancer starts or continues to spread. Even for patients diagnosed at an early stage, if their particular type doesn’t respond well to treatment (like sarcomatoid mesothelioma), they may still face quick metastasis because mesothelioma is aggressive by nature. Recurrence is also common in mesothelioma, which can also see more advanced progression of the disease.

Symptoms of Metastatic Mesothelioma

With more distant mesothelioma progression, symptoms will become more severe and varied. Patients may experience new symptoms that were either mild before or not present at all. As metastasis continues, the symptoms will likely only continue to worsen.

Treating Metastatic Mesothelioma

Malignant mesothelioma can be difficult to treat at any stage and there is no cure. After the asbestos cancer has spread, patients may only have palliative treatment options to improve quality of life. Standard mesothelioma treatments, like chemotherapy and radiation therapy, may still be advised even for patients with metastatic cancer, but the intent won't be the same. Instead, these treatments will be able to help manage pain and discomfort from the symptoms patients are experiencing.

Patients may also find hope in clinical trials, some of which have seen promising results even for those with metastatic cancer. Mesothelioma specialists have seen some success with emerging treatments like immunotherapy and photodynamic therapy that have enabled some patients to live well beyond their prognosis.

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