Epithelial mesothelioma is the most common cell type of mesothelioma and is the most likely to respond well to treatment. Treatment for epithelial mesothelioma may include surgery, chemotherapy, immunotherapy, radiation, or a combination thereof.
Epithelial mesothelioma is one of the three primary cell types of mesothelioma, which also include sarcomatoid and biphasic cell types. Of the three, epithelial mesothelioma cells are the easiest to identify, least aggressive, and most responsive to treatment.
As a result of these factors, patients with this cell type have the best mesothelioma prognosis. Epithelial mesothelioma is also the most common cell type, accounting for approximately 60 percent of all mesothelioma cases.
What is epithelial mesothelioma and what are epithelial mesothelioma cells?
Mesothelioma is cancer of the membranes surrounding the internal organs.
- Pleural mesothelioma – the lungs
- Peritoneal mesothelioma – the abdomen
- Pericardial mesothelioma – the heart
- Tunica vaginalis mesothelioma – the testicles
Epithelial mesothelioma cells are also referred to as epithelioid mesothelioma. Epithelial cells are cancer cells that have the following characteristics.
- A single nucleus per cell
- Approximately the same size and shape
- Tendency to stick together
- Formation of sheets or clumps that spread to other organs less aggressively than
other cell types
- Fast cell reproduction, or mitosis
The fast reproduction rate and the tendency of the cells to stick together may result in rapid growth of tumors, as well as extensive local spread of the cancer within the same organ or in adjacent areas. However, it also makes the cancer less likely to undergo metastasis, or spread to distant parts of the body.
Medically Reviewed By:
Patricia Shelton, M.D.
What causes epithelial mesothelioma?
The primary cause of epithelioid mesothelioma is asbestos exposure. When asbestos is disturbed, the microscopic particles become airborne and are easily inhaled or ingested. Inhaled fibers can lodge deeply in the lungs, where they remain, often for decades, before mesothelioma develops. Ingested fibers can lodge similarly in the lining of the stomach.
Asbestos is virtually indestructible, which is one of the qualities that made it useful in industry. However, this same quality also makes it deadly. The body cannot break it down, so it continues to cause inflammation. Over time, this inflammation can cause damage to cells in the area, leading to cancer.
Epithelial Mesothelioma Prognosis
The median overall survival for epithelioid mesothelioma patients is 14.4 months, with a one-year survival rate of 69 percent.
Symptoms of Epithelial Mesothelioma
One of the reasons for the poor prognosis associated with all types of mesothelioma is the low detection rate during the early stages. Mesothelioma is typically detected after it reaches the later stages, making treatment more difficult.
Early diagnosis of mesothelioma is challenging because the disease tends to cause few symptoms early in the course of the disease. When mesothelioma symptoms do emerge, they tend to be non-specific and mimic less serious, more common conditions such as asthma and pneumonia.
Symptoms may include the following:
Shortness of breath
Pain in the chest wall
How are epithelial mesothelioma cells identified?
Diagnosing any type of mesothelioma requires the use of several tests. Doctors use these tests to distinguish mesothelioma from other types of cancer, such as breast cancer or lung cancer, as well as from other respiratory conditions, such as pneumonia.
According to the American Society of Clinical Oncologists, pleural mesothelioma is usually diagnosed through a CT-guided biopsy or during video-assisted thoracoscopic surgery (VATS). These procedures use advanced technology that allows the surgeon obtain one or more small samples of tissue. A pathologist will examine the tissue under a microscope in order to determine the cell type.
A contrast-enhanced CT scan uses X-rays to visualize the body’s tissues and determine treatment options. Medical providers use CT scans to find fluid around the lung — a condition called a pleural effusion — and other conditions associated with mesothelioma.
MRI may be used to clarify the extent of the disease and the extent of chest wall and organ involvement when considering surgical options. This type of imaging study uses magnetic fields, rather than X-rays, to visualize tissues.
A PET scan can identify distant metastases. This type of scan uses a radioactive tracer to look for cancer cells around the body. Using a PET scan, doctors can determine how widely the cancer has spread.
Doctors may continue to use imaging studies to monitor a patient’s progress. Plain chest X-rays and thoracic ultrasounds can be used to monitor a patient who experiences pleural effusions.
Periodic CT scans are often used to monitor the overall progress of a patient’s cancer. This allows doctors to determine whether the patient’s treatment plan is working or needs to be changed.
Epithelioid Mesothelioma Subtypes
Although all epithelial cells have certain characteristics in common, they do have variations. Epithelioid mesothelioma is classified into subtypes based on which type of epithelial cells the cancer cells most closely resemble.
Well-Differentiated Papillary Mesothelioma
Well-differentiated papillary mesothelioma is a rare subtype that is more common in peritoneal and tunica vaginalis cases. This cell type resembles a long, finger-like growth pattern with a plain layer of epithelioid cells covering the growth.
Well-differentiated papillary mesothelioma umors typically grow superficially, meaning that they rarely penetrate deeply into the body. If they do become more invasive, they are referred to as “Well-differentiated papillary mesothelioma with invasive foci.”
The solid subtype has the lowest overall survival of all the epithelioid mesothelioma subtypes and is one of the most common subtypes of epithelioid mesothelioma, according to Harvard researchers.
A solid epithelioid tumor consists of uniform cells that are round, oval, or polygonal in shape and occur in nests, sheets, or cords. This form of epithelioid mesothelioma may be misdiagnosed as other types of cancer, including solid adenocarcinoma or squamous cell carcinoma. Both of these types could represent either lung cancer or cancer from a different part of the body that has spread to the lung.
Patients with the tubulopapillary subtype of epithelioid mesothelioma — one of the more common subtypes — experience the longest overall survival time of people with epithelial mesothelioma.
Tubulopapillary cells are characterized by a combination of finger-like growth patterns and elongated tubular structures.
The micropapillary type of epithelioid malignant mesothelioma is characterized by small, delicate finger-like growths lined by mesothelial cells. This subtype is more aggressive and tends to spread to the lymphatic system.
Trabecular epithelioid mesothelioma consists of one or two layers of relatively small single-shaped cells that form thin cords and metastasize, or spread, through surrounding tissues, resulting in a shorter overall survival.
Clear cell epithelioid mesothelioma is an exceedingly rare subtype. The cells become transparent because they contain large amounts of glycogen (a type of starch), fats, or both. This subtype is easily confused with other types of tumors.
Adenomatoid epithelioid mesothelioma accounts for just five percent of pleural mesothelioma cases and is an even rarer subtype of peritoneal mesothelioma, according to the Journal of Medical Case Reports. The physical characteristics of these cells can vary. The diagnosis is based on the chemical characteristics of the cells.
It is important to distinguish between adenomatoid tumors, which are benign growths that can occur in the mesothelium, and adenomatoid mesothelioma, which is a malignant disease that can spread around the body and may be fatal.
CytoJournal also reports that this variant typically causes pleural effusion and thickening, which leads to symptoms like shortness of breath. Adenomatoid mesothelioma can also be referred to as microcystic or microglandular mesothelioma. It may be misdiagnosed as “pulmonary/metastatic adenocarcinoma,” meaning that it’s believed to be either lung cancer or cancer from a different part of the body that has spread to the lung.
Pleomorphic epithelioid cells are cells that show nuclear enlargement, hyperchromasia (where the nucleus of the cell looks darker than normal), and multiple different sizes and shapes.
Researchers and practitioners differ as to whether this cell type should be classified as a variant of epithelioid mesothelioma or sarcomatoid mesothelioma. Its aggressive nature and survival rate are more similar to that of sarcomatoid cases. The median survival in studies ranges from 7.3 to 8.1 months.
However, the tendency of the cells to stick together and other distinctly epithelial features support including it as a high-grade epithelioid subtype.
Pleomorphic mesothelioma may be misdiagnosed as the following:
- Pleomorphic carcinomas of the lung
- Anaplastic thyroid carcinoma
- Some sarcomas, especially
The signet ring subtype is a rare variant that typically occurs in pleural mesothelioma but has also been observed in cases of peritoneal mesothelioma, according to Pathology, Research, and Practice. This variant is differentiated by a particular signet ring pattern observed in the cells under a microscope.
Signet ring mesothelioma is challenging to diagnose and may be misdiagnosed as the following:
- Reactive histiocytic hyperplasia (a growth of particular immune system cells)
- Adenocarcinoma (cancer that arises from glandular structures in epithelial tissues)
- Melanoma (cancer that arises in the pigment-producing cells of the skin)
- Lymphoma (cancer that arises in immune system cells)
Since there is no specific marker for signet ring mesothelioma, it is necessary to use a panel of tests to confirm the diagnosis.
The myxoid variant of epithelioid mesothelioma is the most favorable type with a longer-than-average prognosis. In one study conducted by Respiratory Medicine Case Reports, a patient lived with myxoid mesothelioma for over five years without treatment. This can be explained by the slow progression of this subtype.
Small cell mesothelioma is a very rare form of epithelioid mesothelioma with uniform small, round cells, which occur in clumps as small, round tumors, according to Diagnostic Cytopathology. This subtype is generally associated with a poor prognosis due to its propensity to impair organ function and spread locally and to distant body sites, according to DoveMed.
According to BMJ Case Reports, deciduoid mesothelioma consists of large, polygonal or round cells with well-defined cell borders and large nuclei, arranged in a pattern of “solid nests.” Deciduoid cells have been observed in all types of mesothelioma. This type is highly aggressive, with a survival rate of just 32 percent after one year.
Glomeruloid mesothelioma is a rare subtype of epithelioid mesothelioma. It is most commonly seen in pleural mesothelioma, but it has been observed in all types. It is named after the glomerulus of a kidney due to its similar appearance. A glomerulus is a tiny capillary blood vessel structure that is shaped like a ball.
According to DoveMed, this subtype is highly aggressive and difficult to treat. The prognosis is generally poor because the cancer spreads easily to other parts of the body.
Epithelioid Mesothelioma Treatment
Of the three mesothelioma cell types, the epithelioid type is generally the most responsive to treatment. This gives patients with epithelioid mesothelioma more treatment options compared to those with the sarcomatoid or biphasic cell types.
Many patients with epithelioid mesothelioma are eligible for tumor-removing surgery. In carefully selected patients, this type of surgery can significantly extend lifespan. A cancer that surgeons believe could be removed surgically is known as resectable.
However, not all patients are candidates for surgery. Multiple individual factors must be taken into account before moving forward with surgical options. The particular type of epithelioid cells, the stage of the cancer, and the patient’s age and overall medical condition are all important considerations.
For pleural mesothelioma, surgical options include extrapleural pneumonectomy (EPP) or pleurectomy/decortication (P/D).
For peritoneal mesothelioma, a procedure called CRS-HIPEC is most commonly used. This combines surgical removal of cancer tissue with an infusion of chemotherapy drugs into the abdomen.
Chemotherapy, Radiation Therapy, and Immunotherapy
In general, in patients with resectable tumors, surgery is rarely used alone. It’s usually combined with additional treatments like chemotherapy and radiation therapy, in order to maximize the effectiveness of the treatment plan. This is known as multimodal therapy.
While epithelioid mesothelioma patients are the most likely to be eligible for surgery, there are still some whose tumors are considered unresectable, meaning that they can’t be removed surgically. In these patients, chemotherapy has traditionally been the mainstay of treatment.
Immunotherapy is a newer treatment option, which uses the patient’s own immune system to target and destroy the cancer cells. While surgery still offers better outcomes for those who are eligible, immunotherapy may be a good option for epithelioid mesothelioma patients whose tumors are not resectable.
Mesothelioma symptoms can be physically and emotionally taxing, and cancer treatments often have significant side effects that create additional challenges for patients. As a result, cancer specialists recognize the importance of addressing patients’ quality of life as part of the treatment plan.
Because epithelioid mesothelioma tends to be responsive to treatments intended to extend the patient’s lifespan, patients with this cell type often have a treatment plan that’s focused on this goal. However, this does not mean that these patients cannot also receive additional treatments that are intended to address their quality of life.
There are some patients with epithelioid mesothelioma whose treatment plan is focused on the quality of life, rather than on the length of life. This is known as palliative care. Patients whose cancer is in a more advanced stage, those who are elderly or have other major medical problems, and those who prefer not to endure the side effects of aggressive cancer treatments may be treated using palliative care.
Palliative care options may include medications, surgical procedures, and complementary and alternative medicine treatments.
Where to Seek Treatment for Epithelioid Mesothelioma
Mesothelioma treatment is best sought from specialized mesothelioma doctors and treatment centers that specialize in mesothelioma because most oncologists are not experienced in its diagnosis or treatment.
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