There are three types of mesothelioma cells: epithelioid, sarcomatoid, and biphasic. Epithelioid mesothelioma is not only the most common, but it is also the most studied and has the best prognosis.
What is Epithelioid Mesothelioma?
Cancer is the mutation of a previously healthy cell. Cells are programmed to perform a certain duty, to divide, and when they become old, they are programmed to die. Genetic changes to normal cells allow them to ignore their programmed death and continue to divide.
Epithelial cells are one of the four tissue types found in the body. They form the lining for organs, hollow cavities, and our skin. When they are exposed to a carcinogen (like asbestos) it causes genetic changes that turn these cells cancerous. Approximately 50 – 70 percent of all mesothelioma cases are epithelioid, which means it’s the one most studied and has the best prognosis.
Epithelioid mesothelioma is difficult to distinguish from certain other forms of cancer, like adenocarcinoma. Adenocarcinoma is formed from glandular epithelial cells. It is the most common form of lung cancer, but it can occur wherever mucus-producing epithelial cells reside.
It’s important for physicians to rule adenocarcinoma out prior to treatment, as the treatment protocols are different from mesothelioma.
Recently, researchers have discovered various stains that, when applied to the cells and then viewed under a microscope, reveal the type of cancer the patient has. Research continues to be done to further reduce the chances of an incorrect diagnosis.
Where It Occurs
Epithelial mesothelioma most commonly occurs in the pleural cavity – the area around lungs. In fact, 70 percent of all cases of pleural mesothelioma are epithelioid. The other common locations for mesothelioma (the abdomen, and very rarely, the lining of the heart) are more commonly sarcomatoid or biphasic.
How It Develops
Epithelioid mesothelioma develops when epithelial cells mutate into cancerous cells – that is, those cells that no longer serve their original purpose and have uncontrolled division. With only the rarest exception, asbestos exposure causes the mutation.
The asbestos type that is most likely to cause mesothelioma has tiny, needle-like fibers that pierce the lungs when inhaled. Over time they work their way through the inside of the lung to the outer lining. This causes inflammation and irritation in the lining of the pleural cavity, which is composed of epithelial cells. Gradually the epithelial cells undergo genetic mutation and become cancerous.
Occasionally asbestos can work its way into other organs and cause mesothelioma in different locations, but this is not common.
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Epithelioid Mesothelioma Subtypes
Scientists group the following cells types under epithelioid mesothelioma, but they can have their own traits and levels of aggression. Also, some, like small cell, are epithelioid about half the time, but can also be biphasic, which means it contains a mixture of epithelioid and sarcomatoid cells.
Otherwise known as glandular or microglandular mesothelioma, these cells can be flat or cube-like and can line glands, which can make it difficult to differentiate from adenocarcinoma.
Small Cell Mesothelioma
This very rare form of epithelioid mesothelioma was first discovered in 1992. It looks very similar to other small cell forms of cancer like small cell lung carcinoma. Pathologists diagnose small cell mesothelioma through cytologic analysis (looking at the cells through magnification).
This is incredibly rare, and usually benign. It is found in women of childbearing age and is traditionally found in the abdomen. The disease forms a mesothelial-lined cyst that is surrounded by fibrous tissue. Surgery is the most common treatment.
This very rare epithelioid mesothelioma occurs predominantly in the abdomens of women. It is technically cancerous, but it is not aggressive, and it rarely metastasizes. After surgery, most patients do not have a recurrence. It is sometimes called well-differentiated papillary mesothelioma (WDPM).
This rare sub-type can occur in the abdomen of females who have not been exposed to asbestos, or in the lining of the lungs of men and women who have. This cancer is treated the same as regular epithelioid mesothelioma, but it can be extremely aggressive, depending on the shape of the cells.
Epithelioid Mesothelioma Incidence, Prognosis and Survival Rates
Asbestos causes most cases of epithelioid mesothelioma. Asbestos takes time to cause cancer, and thus, most patients are diagnosed later in life. Mesothelioma can take 20 – 50 years to develop after asbestos exposure.
Men are more likely to contract epithelioid mesothelioma because most asbestos exposure is work-related. The high-risk industries were predominately construction and have been traditionally staffed by men.
- Age: The younger the patient when the mesothelioma is diagnosed, the better the prognosis.
- Gender: Statistically, female patients live longer than males.
- Histology: Histology is the cell type. Mesothelioma patients with cancerous epithelioid cells have a better prognosis than those with sarcomatoid or biphasic cells.
- Metastasis: Cancer that hasn’t spread to the surrounding tissues or organs provides a better chance of treatment.
- Stage: The more advanced the cancer, the lower the survival rates.
Prognosis and Staging
Cancer stages are based on the TNM classification, which rates the patient’s cancer on three factors: Tumor, Lymph Nodes, and Distant Metastasis. Essentially, researchers and physicians want to know to what extent the tumor has formed, and, if it has traveled, how far and how deeply embedded in other tissues has it become. Patients are told their cancer falls into a “stage” of 1 through 4. These stages are a cumulative assessment of the TNM classification.
One study broke down the difference in prognosis and survival between patients with epithelioid mesothelioma and sarcomatoid mesothelioma. All of these patients received surgery and a mix of chemotherapy and radiation therapy.
- Patients with epithelioid mesothelioma had a 2-year survival rate of 50 percent, and a 3 year survival rate of 42 percent.
- Patients with the rarer sarcomatoid mesothelioma had a 2-year survival rate of 7.5 percent, and none lived past 25 months.
Epithelioid Mesothelioma Symptoms and Diagnosis
Due to the location of the cancer, mesothelioma in the chest cavity (pleural) and that in the abdomen (peritoneal) will differ.
- Chest pain (side)
- Unintended weight loss
- Swelling of the face or upper extremities
- Unable to “catch your breath”
- Pain in the abdomen
- Abdominal Swelling
Most patients will begin to feel some symptoms and seek medical help. If the patient has a history of asbestos exposure, the doctor may suspect mesothelioma, but she will order follow-up tests to be sure.
The first step will be to image the patient’s chest with x-ray, CT scan, PET scan, MRI, and/or echocardiogram. If masses are found, then further tests will determine if they are cancerous, and then what specific kind. These tests will look for specific biomarkers.
Biomarkers are objective and measurable biological markers of disease. The best biomarker is a blood/pleural fluid test. It looks for soluble mesothelin-related peptides (SMRPs). SMRPs are a byproduct of mesothelioma tumors.
While this is the “best” biomarker, it isn’t good enough to positively identify every case, nor always distinguish it from other forms of cancer. Many physicians continue to use this test to track the progression of the disease after diagnosis.
Physicians use histology, which is studying the microscopic structure of the tissue, to positively diagnose and distinguish what kind of mesothelioma the patient has. Histology is considered the “gold standard” for positively diagnosing this disease.
Treatment for Epithelioid Mesothelioma
As the most common form of mesothelioma, epithelioid mesothelioma has three primary treatment options available. When more than one of these therapies are used, this is called multimodal treatment.
There are three surgeries available for epithelioid mesothelioma patients.
For patients who are in otherwise good health, this potentially curative surgery removes the entire lung, mesothelium (lung lining), half the diaphragm, and pericardium (heart lining) on that side. This is a major surgery with a high rate of complications, but if the patient meets the requirements, some researchers argue it can potentially cure the disease.
This surgery removes the tumors and the lining of the lung and chest cavity on that side. If the cancer is caught early enough, this could be curative, but this procedure can also be used to reduce the pain and symptoms of advanced mesothelioma.
This is a form of P/D that removes as much of the cancer tumor as possible.
There are two categories of chemotherapy currently in use for mesothelioma patients.
This therapy can reduce the size or decrease the advancement of mesotheliomas, but this positive response does not last.
These drugs attack what makes cancer cells different than healthy cells. This relies on understanding the particularities of that cancer, as the genetic changes between two patients with the same cancer may differ.
Radiation therapy is not usually very effective on mesothelioma because the tumor is rarely contained to one area. This makes it difficult or impossible to concentrate the radiation waves at only the affected tissue.
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Epithelioid mesothelioma has received more research than any other form of the disease, because it is the most common variety. Some experimental treatments have shown promising results.
Scientists remove immune cells from the patient’s body and modify them in the lab to react with the cancer cells. They are reinfused into the patient with a blood transfusion. This is still in clinical trials.
Researchers are running tests on using modified viruses to inject new genes into the mesothelioma cancer cells. These genes make the cancer cells easier to kill. Preliminary results show the cancer tumors slowing or even shrinking after receiving this treatment.Sources
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