Epithelioid mesothelioma is the most common cell type and is diagnosed in about 70 – 80% of all cases.
As with all other types of malignant mesothelioma, epithelioid mesothelioma is caused by asbestos exposure. Compared to other cell types associated with mesothelioma, biphasic and sarcomatoid, epithelial is the most studied form of the rare cancer. Epithelioid cells are slow to grow and respond more favorably to treatment than sarcomatoid cancer cells. On average, patients have a more favorable prognosis compared to other cell types, with an average life expectancy of one to two years.
Epithelioid Cell Structure
Epithelial cells make up one of four types of tissues in the body. Epithelial tissue is found on the skin’s surface, in the linings of hollow organs and blood vessels, and along the lining of internal cavities, including the pleura. When the cells are exposed to a carcinogen, like asbestos fibers, they mutate and become cancerous.
Normal epithelial cells come in several different shapes and can be found in single or multiple layers, depending on where they are. Although some epithelial cells are cube-shaped or columnar, the ones most commonly found in the lining of the lungs are squamous cells, which are flat and allow for molecules to pass through.
Epithelioid mesothelioma cells are also recognizable because of how they group together. The cells form in small clusters, and may be round or oval with more than one nucleus in each cell.
Rare Epithelial Cell Types
In addition to the common epithelioid cell type, pathologists have identified various rare subtypes that have developed in some cases..
- Adenomatoid mesothelioma: Also known as glandular or microglandular mesothelioma, the shape of these cells are either flat or cube-like and can be benign or malignant. It forms in gland-like structures.
- Adenoid cystic mesothelioma: Most common 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: A very rare form of cancer, this mesothelioma typically develops in the abdomen, but can also form in the lining of the lungs. The cancer’s exact cause is currently unknown, and it most often is 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 in the genitals of both men and women. Papillary mesothelioma is slow to metastasize and studies have found survival times ranging from 36 to 180 months.
- Small cell mesothelioma: Sometimes mistaken for small cell lung cancer, this subtype forms in the peritoneum and pleura. Small cell mesothelioma is usually diagnosed in biphasic tumors, which contain both epithelial and sarcomatoid cells.
Diagnosing Epithelioid Mesothelioma
Epithelioid mesothelioma presents with a variety of symptoms, but some are location specific based on where the cancerous cells develop. In addition to the cancer’s location, the presence and severity of symptoms depends on a patient’s overall health, age, the cell type and the stage at diagnosis.
- Coughing and hoarseness
- Abdominal or chest pain
- Fever and fatigue
- Fluid buildup near the lungs or abdomen
- Nausea and vomiting
- Difficulty breathing
- Unexplained weight loss
The diagnostic process for epithelioid mesothelioma typically begins with a series of imaging tests, including CT scans, PET scans, and MRIs, along with blood testing. Blood tests can identify specific biomarkers to help determine if mesothelioma cells are present. This method checks for soluble mesothelin-related peptides (SMRPs), which are produced by mesothelioma tumors. According to a 2015 study, mesothelin levels in those with mesothelioma are higher than those who are healthy or diagnosed with a benign disease.
After these tests, a biopsy will be performed to confirm a diagnosis. A biopsy can be a non-surgical or surgical procedure to take a tissue sample for analysis. Lab tests can determine the subtype of mesothelioma cells, identify stage, determine malignancy and definitively confirm mesothelioma. The pahtologists also typically perform analysis called immunohistochemistry, which employs different types of antibodies to test for the presence of particular antigens in cell tissue that aid in confirming the diagnosis.
Immunohistochemistry is one way to differentiate mesothelioma from other cell types and malignancies, like adenocarcinoma. For example, antibodies including calretinin, D2-40 and WT1 are used to identify mesothelioma in patients, while adenocarcinoma will test positive for other antibodies like TTF-1, Napsin A, CK20 and CEA. When these antibodies are used in combination, they can help a pathologist correctly diagnose the disease.
Epithelioid Mesothelioma Prognosis
A patient’s cell type also plays a role in their prognosis. Those with epithelioid cancer cells have a better prognosis and overall life expectancy than those with other cell types. On average, patients survive one to two years after diagnosis. A 2017 study suggested epithelial mesothelioma patients who receive multimodal treatment have a median survival time of 23.4 months, compared to median survivals of six and 12 months for sarcomatoid and biphasic mesothelioma, respectively.
The prognosis for epithelioid mesothelioma patients is largely dependent on a number of factors, including the location and staging of the cancer, the patient’s age, their general health and if they have any pre-existing conditions.
Treatment Options for Epithelioid Mesothelioma
Among the mesothelioma treatments currently available are several forms of surgery, chemotherapy and radiation therapy. In many cases, patients will undergo a multimodal treatment plan, which occurs when two or more types of treatment are combined. These therapies may be applied curatively or palliatively for patients with more advanced disease.
It has been shown in several studies that when epithelioid mesothelioma patients undergo multimodal or trimodal therapies, they have better outcomes than patients with other cell types. In a 2018 research study, patients with epithelial or biphasic mesothelioma survived 20.9 and 14.7 months with surgery, compared to only 11.2 for those with sarcomatoid. This is partly because epithelial cells are slower to metastasize than sarcomatoid cells, making them easier to surgically remove.
Radical surgeries, including pleurectomy/decortication (P/D) and extrapleural pneumonectomy (EPP), are available options for patients with epithelial pleural mesothelioma who are in good overall health and diagnosed early. According to a 2017 study, mesothelioma patients receiving P/D or EPP surgeries saw survival averages of 17 and 24 months, respectively.
Chemotherapy is considered the standard of care when treating epithelial mesothelioma and may be used with surgery or as a first-line therapy when surgery isn’t a viable option. A recent study found that adding the targeted antibody bevacizumab (Avastin) to pemetrexed and cisplatin chemotherapy improved survival over patients undergoing chemotherapy alone.
Immunotherapy treatments have also shown promise in treating mesothelioma, and a recently reported study confirmed the activity of nivolumab (Opdivo) administered alone or in combination with ipilimumab (Yervoy) in patients with mesothelioma who had already received pemetrexed-based chemotherapy. Pembrolizumab (Keytruda) has also shown activity in reported trials.
Patients with epithelioid mesothelioma may also be able to partake in clinical trials to find additional treatments, like immunotherapy and gene therapy, which may extend survival.
Author: Linda Molinari
Editor in Chief, Mesothelioma Cancer AllianceRead about Linda
Reviewer: Dr. James Stevenson
Medical Reviewer and Thoracic Medical OncologistRead about Dr. Stevenson
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