Malignant Mesothelioma

Malignant Mesothelioma

Malignant mesothelioma is a cancer that affects the thin tissue layer that covers your internal organs, called the mesothelium. Physicians divide malignant mesothelioma into types dependent on the area of the mesothelium affected.
The most common form of malignant mesothelioma is pleural mesothelioma, cancer of the pleura, the lining of the lungs. Peritoneal mesothelioma, the second most common form, is a cancer of the lining of the abdomen, and accounts for between 10 and 20 percent of malignant mesothelioma diagnoses. In much rarer cases, malignant mesothelioma can occur in the pericardium, the lining of the heart, or the tunica vaginalis, the lining around the testicles.
Malignant mesothelioma is caused by exposure to asbestos. This form of cancer develops when asbestos fibers are inhaled and lodge in the pleura, peritoneum, or pericardium, causing scarring and inflammation, and - eventually - tumors.
Not everyone who is exposed to asbestos will develop malignant mesothelioma. Some individuals may have no reaction to the toxic mineral at all while others may develop less severe asbestos-related diseases such as asbestosis or pleural plaques.

Types of Malignant Mesothelioma

Histologically, malignant mesothelioma is divided into three types: epithelioid, sarcomatoid, and biphasic. These classifications pertain to the shape and structure of the cancer cells. All are treated similarly though some are handled more aggressively than others as they offer a shorter lifespan. Each case is considered individually

Epithelioid Malignant Mesothelioma

In terms of cellular histology, there are three different types of mesothelioma cells: epithelioid, sarcomatoid, and biphasic. Epithelioid mesothelioma is the most common of the three types of malignant mesothelioma, occurring in between 50% and 70% of cases.
Epithelioid mesothelioma cells are given this name because, when viewed under a microscope, they have the appearance of epithelial cells. These are cells which line structures and cavities located throughout the body. Mesothelial cells are themselves a type of epithelial cell, and it is these cells that become cancerous when malignant mesothelioma develops within the pleura, peritoneum, or pericardium. Epithelioid mesothelioma cells tend to have a well-defined, uniform shape when viewed under a microscope.
An important point to note is that malignant epithelioid mesothelioma cells very closely resemble cells of another type of cancer known as adenocarcinoma, which can develop in the lungs or in other vital organs. This type of cancer also originates in epithelial tissue. When adenocarcinoma develops in the lungs, it can often spread to the mesothelial lining of the lungs (the pleural membrane).
For these reasons, those diagnosed with adenocarcinoma who have been exposed to asbestos in the past should seek a second opinion so as to insure accurate diagnosis.

Prognosis and Treatment

Generally, each of the three types of mesothelioma - epithelioid, sarcomatoid, and biphasic - are treated in much the same way as treatment is based on the location and stage of the cancer, rather than the type of cells involved.
However, there are distinct differences in the way each type of cancer responds to treatment. In general, patients with malignant epithelioid mesothelioma have a better prognosis than patients with either sarcomatoid or biphasic mesothelioma so treatment may not be as aggressive at the onset.

Mesothelioma - Malignant - Sarcomatoid

Cancer specialists use a variety of different methods to categorize malignant mesothelioma. The most well-known of these to non-medical people is that the cancer is categorized according to its point of origin in the body. For example, pleural mesothelioma develops in the lining of the lungs, pericardial mesothelium in the lining of the heart, and peritoneal mesothelioma in the lining of the abdominal cavity.
Malignant mesothelioma and other types of cancer are also categorized according to have far advanced each case of cancer is, in terms of factors such as the size of tumors, and whether cancer has spread to lymph nodes or other locations. To read more about how cancers are categorized in this way, please see "Mesothelioma - Staging Systems - Overview."
In addition, malignant mesothelioma and other cancers are categorized according to the size, shape and general appearance of cells when viewed under a microscope, and the types of proteins that can be detected on the surface of the cells. This type of categorization is called histology, or histopathology.
Each of these systems of categorization provides mesothelioma specialists with important information that they use to determine the exact type of cancer cells they are dealing with in a given case. This information is then used to determine how best to treat each patient on an individual basis.

Biopsy and Histopathology

Patients who undergo medical evaluation to determine if they have malignant mesothelioma will undergo a variety of medical tests that determine the location and nature of the cancer. One of these is a biopsy of cells that are suspected to be cancer cells. During a biopsy, samples of suspected cancer cells are removed from several different locations in the tumor site. These cell samples are then evaluated in a laboratory to determine whether the cells are malignant, and what type of cells they are. For more information about biopsy procedures a mesothelioma patient might undergo, please see "Mesothelioma - Surgery - Biopsy."
In the laboratory, cells that are suspected to be cancerous are tested in two ways. First, they are viewed under a microscope to determine their general appearance. Second, they are tested for the presence of oncoproteins and other molecules that are produced by specific types of cancer cells.
When viewed under a microscope, mesothelioma cells, and other types of cancer cells, can be distinguished from normal healthy cells because of their shape and other differences in appearance. Further tests are needed to determine the exact nature of the cells, however. These tests evaluate the types of proteins that are present on the surface of the cells. When mesothelial cells become malignant and turn into mesothelioma cells, they begin producing different types of proteins, and some of these are present on the surface of the cells. Examining the types of proteins present allows a histologist to determine if the cells are malignant mesothelioma, another type of cancer, or healthy cells.

Malignant Sarcomatoid Mesothelioma

Malignant sarcomatoid mesothelioma is the least common of the three cellular mesothelioma types. This form of mesothelioma accounts for between 10% and 15% of cases. When viewed under a microscope, malignant sarcomatoid mesothelioma cells appear as elongated spindle-shaped cells that are irregularly shaped and often overlap one another.
It's important to know that malignant sarcomatoid mesothelioma is sometimes difficult to diagnose on the basis of histological methods. For example, cells of another type of cancer called pulmonary sarcomatoid carcinoma are very similar in appearance and other characteristics to malignant sarcomatoid mesothelioma.
For this reason, if you are diagnosed with cancer and you know that you have been exposed to asbestos at some time in the past, obtaining a second diagnostic opinion may be important. Different types of cancer vary widely in terms of prognosis and treatment options, and if you are misdiagnosed, you may not receive the most appropriate treatment for your cancer.

Prognosis and Treatment

Each of the three types of mesothelioma - sarcomatoid, epithelioid, and biphasic - are generally treated in the same way. Treatment is not based on the specific type of cells involved, but instead on the location of tumors and the stage of the cancer. Please see "Mesothelioma Treatment" for further information about treatment options for this type of cancer.
Even so, each type of cancer responds to treatment very differently. In general, patients with malignant sarcomatoid mesothelioma have a poorer prognosis than patients with epithelioid mesothelioma, because sarcomatoid cancers are more aggressive and more resistant to treatment. However, the general prognosis for all types of mesothelioma is usually poor, and the difference in prognosis between sarcomatoid, epithelioid, and biphasic cancers may amount to as little as only a few months.

Malignant Biphasic Mesothelioma

In histological terms, there are three different types of mesothelioma: sarcomatoid, epithelioid, and biphasic. Malignant biphasic mesothelioma - or "mixed" mesothelioma - accounts for between 20% and 40% of all mesothelioma cases, making it the second most common type of mesothelioma.
Biphasic mesothelioma tumors are made up of a combination of both epithelioid and sarcomatoid cells. These are typically arranged in groups within a tumor, rather than appearing as an even mixture of cells. For this reason, during diagnosis, several different samples are taken from different locations within a tumor using a biopsy, to ensure that a correct diagnosis can be made, as this cancer does not have a unique cellular structure.

Prognosis and Treatment

Treatment for mesothelioma is not based on the type of cells involved, but instead on the location of tumors and the stage of the cancer. While cell type does not determine treatment options, each type of cancer responds to treatment in different ways.
In general, patients with biphasic mesothelioma have a poorer prognosis than patients with epithelioid or sarcomatoid mesothelioma, because biphasic tumors tend to be more treatment-resistant. Because of this, biphasic malignant mesothelioma is often treated more aggressively in hopes of extending the life of the patient.