What Is Epithelioid Mesothelioma?
Epithelial cells make up one of four types of tissues naturally found in the body. Epithelial tissue is located on the skin’s surface, in the linings of hollow organs and blood vessels, and along the lining of internal cavities.
When an individual is exposed to asbestos fibers, epithelial cells can mutate and become cancerous. Epithelioid mesothelioma is the most common form of the disease. The cell type is found in about 70 – 80% of all mesothelioma cancer patients.
Normal epithelial cells differ in shape and can be found in single or multiple layers, depending on where they are located in the body. When the cells mutate, they may also develop in the lining of the lungs, abdomen or heart.
Epithelioid cells can present in a variety of shapes, including:
- Squamous (flat)
Squamous cells are commonly found in the lining of the lungs, also known as the pleura.
Epithelioid mesothelioma cells are also recognizable compared to other mesothelioma cell types because of how they adhere to each other. The cells form in small clusters and may be round or oval. The cells can also be identified by their visible nuclei.
Epithelioid cells typically divide faster than other cells. However, due to the way the cells form in clusters, they are slower to metastasize compared to other cell types.
Epithelioid Mesothelioma Symptoms
Epithelioid mesothelioma presents with a variety of symptoms, depending on where the cancer develops. The presence and severity of symptoms also depend on a patient’s overall health, age, the cell type and the stage at diagnosis.
Common Symptoms of Epithelioid Mesothelioma
- Abdominal or chest pain
- Anemia (low iron)
- Coughing and hoarseness
- Difficulty breathing
- Fever and fatigue
- Fluid buildup near the lungs or abdomen
- Low blood oxygen levels
- Nausea and vomiting
- Unexplained weight loss
Because epithelioid mesothelioma does not spread as quickly as sarcomatoid cells, patients may not experience severe symptoms until a later stage of disease.
Resources for Mesothelioma Patients
Diagnosing Epithelioid Mesothelioma
The diagnostic process for epithelioid mesothelioma typically begins with a series of imaging tests. These tests may include X-rays, CT scans, PET scans or MRIs. If a tumor or abnormality is detected, a blood test may be ordered. Blood tests can identify specific biomarkers to determine if mesothelioma cells are present.
A biopsy will be performed to confirm a diagnosis. A biopsy can be a non-surgical or surgical procedure to remove a tissue sample for analysis. Lab tests can determine the type of mesothelioma cells, as well as identify stage and malignancy.
A pathologist may also perform an analysis called immunohistochemistry, which is a staining technique that uses various antibodies to test for particular antigens in cell tissue. Immunohistochemistry can identify cell type and differentiate mesothelioma from other malignancies, such as adenocarcinoma.
Antibodies including calretinin, D2-40 and WT1 are used to identify epithelioid mesothelioma in patients. When these antibodies are applied in combination, they can help a pathologist accurately diagnose the disease.
Rare Epithelial Cell Types
In addition to the common epithelioid cell type, pathologists have identified various rare subtypes that develop in some patients. These subtypes may have limited treatment options and worse prognoses compared to standard epithelial mesothelioma.
- Adenomatoid mesothelioma: Adenomatoid cells, also known as glandular or microglandular mesothelioma, form in glandular structures. The cells are commonly flat or cubed shape and can be benign or malignant.
- Adenoid cystic mesothelioma: This rare form of mesothelioma is most commonly found in the peritoneal or pleural cavities. Cystic cells are often benign, though malignancies can sometimes form. Cystic mesothelioma is more commonly diagnosed in young women, particularly those of child-bearing age.
- Deciduoid mesothelioma: This rare form of mesothelioma typically develops in the abdomen, but it can also form in the lining of the lungs. The cancer’s exact cause is currently unknown, and it is most often diagnosed in women.
- Well-differentiated papillary mesothelioma (WDPM): This type of mesothelioma is not related to asbestos exposure and usually affects young women. It can form in the pleura, peritoneum and genitals of men and women. Papillary mesothelioma is slow to metastasize. Studies have found survival times ranging from 36 – 180 months.
- Small cell mesothelioma: This subtype is sometimes mistaken for small cell lung cancer. It forms in the peritoneum and pleura. Small cell mesothelioma is usually diagnosed in biphasic tumors, which contain epithelial and sarcomatoid cells.
Epithelioid Mesothelioma Prognosis
A patient’s cell type also plays a role in prognosis. Patients with epithelioid cancer cells have a more favorable prognosis and overall life expectancy than those with other cell types. On average, patients with epithelioid mesothelioma survive one to two years after diagnosis.
One 2017 study examined the survival times of epithelial mesothelioma patients who underwent multimodal treatment, as well as patients with sarcomatoid and biphasic cell types. Researchers found:
- Epithelial mesothelioma patients have a median survival time of 23.4 months
- Biphasic mesothelioma patients have a median survival time of 12 months
- Sarcomatoid mesothelioma patients have a median survival time of six months
The prognosis for epithelioid mesothelioma patients is dependent on a number of factors, including the location and staging of the cancer, as well as the patient’s age, general health and pre-existing conditions.
Epithelioid Mesothelioma Treatment
Epithelioid mesothelioma treatment may include surgery, chemotherapy and radiation therapy. In many cases, patients will undergo a multimodal treatment plan, which occurs when two or more methods of treatment are combined. Some procedures can also be used as palliative treatments, which can lessen symptoms for patients.
Epithelial pleural mesothelioma patients diagnosed at an earlier stage may be eligible for surgery, including pleurectomy/decortication (P/D) and extrapleural pneumonectomy (EPP). These surgeries involve removing cancerous tissue from the lung and surrounding areas.
In a 2018 study, patients with epithelial or biphasic mesothelioma survived 20.9 and 14.7 months with surgery, respectively, compared to 11.2 months for those with sarcomatoid. This is partly because epithelial cells are slower to metastasize than sarcomatoid cells, making them easier to surgically remove if caught early.
Along with surgery, patients may be candidates to receive multimodal treatment, which is a combination of treatments that may improve survival times. Chemotherapy is considered the standard of care when treating epithelial mesothelioma. It may be used with surgery, or as first-line therapy when surgery isn’t a viable option.
Immunotherapy treatments have also shown promise in treating mesothelioma. A recent study found that adding the immunotherapy drug bevacizumab (Avastin®) to different forms of chemotherapy improved survival compared to patients who underwent chemotherapy alone. Patients treated with chemotherapy survived 16 months on average, while patients treated with chemotherapy and immunotherapy survived nearly 19 months.
Patients with epithelioid mesothelioma may also be able to partake in clinical trials to find additional treatments, such as gene therapy, that may extend survival.