Metastasis is the medical term for when cancer spreads to distant sites. Knowing how far mesothelioma has metastasized is critical because it helps doctors put together the most effective treatment plans for controlling or stopping the spread of the disease.
What is Metastasis?
The word “metastasis” comes from the Greek “displacement” or “movement to the next place.” Metastasis occurs when mesothelioma cells move from their point of origin into other surrounding tissues where new tumors begin to grow. Metastasis is the key factor in determining how advanced a case of mesothelioma is, and what the available treatment options are.
As mesothelioma advances, curative treatments such as surgery may become less feasible, and more palliative treatments focused on easing symptoms and reducing the rate of mesothelioma cell growth become more necessary. Early diagnosis and treatment are essential to preventing metastasis.
How Does Metastasis Occur?
As mesothelioma cells originating in the lining of vital organs begin to grow, a cell or small cluster of cells may break away from the point of origin and travel through the lymphatic system or bloodstream eventually adhering to another nearby location. These cells begin to replicate, and a new tumor grows.
Even though metastatic tumors grow in another organ, they are still mesothelioma cells and require mesothelioma treatment protocols as opposed to being treated as another type of cancer. For example, if pleural mesothelioma metastasizes to the liver, it is not considered to be liver cancer.
Factors that determine how and where metastasis may occur include cell type and originating location.
- Pleural mesothelioma, originating in the lining of the lungs, is central to many vital organs and may travel to the diaphragm, abdomen, adrenal glands, liver, bone and/or brain.
- Peritoneal mesothelioma, originating in the abdominal tissue lining, may travel to the liver, ovaries/prostate and/or intestines.
- Pericardial mesothelioma, originating in the lining of the heart may travel to either the lungs and/or abdomen.
While the above is not an exclusive list of where mesothelioma can spread, distant metastases are certainly rarer. Cell type is a greater influencer on how and how far mesothelioma may spread.
Metastasis in Epithelioid Cell Type
Epithelioid mesothelioma cells are smaller, rectangular shaped cells that have a tendency to form in a more even and organized pattern. Epithelioid cells are most likely to travel to very close nearby locations or to travel shorter distances via the lymphatic system. The lymphatic system transports fluid and white blood cells throughout the body and is a critical element of the immune system. The lymphatic system contains clusters of nodes that act as filters or gates to prevent pathogens from passing on to other areas; a key reason that epithelioid cells are less likely to travel to distant regions of the body.
Metastasis in Sarcomatoid Cell Type
Sarcomatoid mesothelioma cells are larger and longer cells with a spindle-like or cylindrical shape. Sarcomatoid cells grow more aggressively and faster than epithelioid cells. Due to their shape, size and organization, sarcomatoid cells are more likely to travel in lumps via the vascular system or bloodstream. Travel via the vascular system may carry cells further away from their point of origin than travel via the lymphatic system.
Metastasis in Biphasic Cell Type
Biphasic mesothelioma is made up of both epithelioid and sarcomatoid cell types. Biphasic mesothelioma will behave in the modality indicated by the dominant cell type; for example, if the biphasic mesothelioma is comprised by a majority of epithelioid cells—any metastasis will most likely be local and travel via the lymphatic system.
Advancement of mesothelioma is classified by a staging system. However, there is no universal staging system for mesothelioma; while some doctors base their staging systems on cell type and location, other doctors may use a system based on what treatments are acceptable and available considering the condition of the patient. This is why it is essential to seek treatment from a specialist that focuses on your type of mesothelioma.
All pleural mesothelioma staging systems include 4 stages. Stages 1 and 2 are considered to be the early stages of mesothelioma in which tumors are beginning to form and deepening into the local underlying tissues. This may occur decades after exposure to asbestos, and symptoms may not clearly present until the late into the early stages of mesothelioma. In the case of pleural mesothelioma, these are the stages in which the cancer remains unilateral (or isolated to one side of the lungs), and has not spread past the lung tissue or diaphragm. During stages 1 and 2, curative treatment options like cytoreductive surgery (often followed by chemotherapy and radiation) are viable options.
Stages 3 and 4 are considered to be advanced mesothelioma and metastasis has occurred. Due to the challenges in accurately diagnosing mesothelioma, these are frequently the stages in which a first diagnosis is made. In stage 3, metastasis remains relatively local. In the case of pleural mesothelioma, this means that there may be some moderate spreading to the pericardium (the tissue lining the heart), the diaphragm, surrounding fatty tissues, local lymph nodes and the inner lining of one lung, but the cancer remains unilateral. Symptoms increase in severity and palliative care becomes necessary to decrease chest pain, recurring dry cough and shortness of breath. At stage 3, surgery is generally still an option; however, must be more extensive. Post-surgical chemotherapy and radiation treatment have yielded a better survival rate than surgery alone.
Stage 4 malignant mesothelioma (or end-stage mesothelioma) is characterized by significant metastasis to one or more areas (in the case of pleural mesothelioma, both lungs are likely now affected), and patients may be too weak to undergo aggressive surgical treatment. At this stage, any surgical treatment is typically part of a palliative care regimen (such as one of a variety of centesis procedures that remove fluid build-up and alleviate pressure). Curative surgery is no longer possible as the spread of the disease has surpassed the breadth and depth of what a patient can endure. Chemotherapy, radiation therapy and/or immunotherapy may be recommended to increase life expectancy.
Technological advancements in both the curative and palliative treatment of mesothelioma are constant, and a medical professional specializing in the care of your type of mesothelioma may be able to advise you as to eligibility for clinical trials. Many clinical trials have demonstrated success in significantly increasing life expectancy. As with any clinical trial, positive results are not guaranteed.
While three different staging systems are most commonly used for the classification and designation of treatment protocols for pleural mesothelioma (TNM, Bringham & Butchart systems), those systems to classify peritoneal and pericardial mesothelioma remain somewhat less developed due to the rarity of these conditions. The relationship between stage and severity, however, remains the same. The best way to understand the advancement of your mesothelioma is to work closely with a specialist that focuses on your type of mesothelioma and to seek a second opinion on treatment options.
Metastasis and Prognosis
While metastasis and prognosis are inversely related (meaning that prognosis declines as the stage of mesothelioma increases), no two cases of mesothelioma are exactly alike. Statistics are not generally reliable in making an assumption about prognosis.
Each case of mesothelioma progresses at a unique rate, and no single treatment combination or modality is universally effective. Only you and your doctor can make informed decisions about your treatment plan and your prognosis. What is certain is that a high level of patient comfort, and a positive outlook and attitude vastly improve both life expectancy and quality of life.
For more information on staging mesothelioma and how metastasis affects your prognosis, contact our Patient Advocates today.