Mesothelioma is a rare type of cancer caused by asbestos exposure. There are three types of cells which may cause mesothelioma to develop. Up to 70 percent of all mesothelioma cases involve the epithelioid type cells. Epithelioid mesothelioma is the most treatable type and often has the best prognosis.
Epithelial cells make up the lining of major body cavities and form the structure of the lungs. They are also the type of cells that make up the skin surface, providing protection against the environment. When they are healthy, they divide slowly with new cells forming only as needed but when exposed to asbestos, epithelial cells may become cancerous.
The latency time between asbestos exposure and the development of mesothelioma may be as much as 20 to 50 years. During that time, asbestos fibers have lodged in the epithelial tissue, resulting in inflammation and DNA mutation which causes the cells to begin dividing uncontrollably. Epithelioid mesothelioma is more common but may be more treatable, with a better prognosis than other cell types.
Epithelioid Mesothelioma Characteristics
Epithelial cells are some of the most common cells in the body. The cells cover the skin surface and the linings of many organs including the stomach, intestines, kidneys and other organs. They also comprise the “epithelial layer” of the mesothelium and make up much of the structure of the lungs. When these cells become cancerous, epithelioid mesothelioma may develop.
Epithelioid mesothelioma accounts for about 70 percent of all mesothelioma types. It is generally equally common in both sexes but one certain sub-type of epithelioid mesothelioma known as “well-differentiated papillary mesothelioma” is more common in women.
Epithelial cells have a distinctive appearance of an oblong or egg-type shape but may vary slightly with sub-type. They are uniform in size and shape and also have a distinctly visible nucleus which is easy to identify with magnification. Once epithelial cells become cancerous, they are known as epithelioid cells.
Because epithelial cells serve as linings and protective layers where cells are prone to “slough” off as on the skin surface, they divide more frequently than other cells in the body. In order to provide protection as a lining, the cells also stick together quite readily. These characteristics contribute to faster tumor growth but less metastasis as epithelioid mesothelioma cells are less likely to break off the tumor.
Epithelioid Mesothelioma Diagnosis
Up to 70 percent of all pleural mesothelioma diagnoses are due to epithelioid cell types but they are also found in peritoneal mesothelioma and other types as well.
Epithelioid mesothelioma cells appear to be similar to cancerous cell types of adenocarcinoma, ovarian cancer, breast cancer and other carcinomas which affect the linings of organs, including the lungs. The cells are similar enough to lung cancer cells that any patient with a adenocarcinoma lung cancer diagnosis should also be examined for pleural epithelioid mesothelioma.
Symptoms of Epithelioid Mesothelioma
As most epithelioid mesothelioma cases involve the pleura, most patients will have symptoms of pleural mesothelioma such as:
- Shortness of breath
- Difficulty breathing
- Chest pain
- Difficulty swallowing
Some patients with epithelioid mesothelioma are peritoneal cases which may have symptoms of:
- Shortness of breath
- Abdominal pain
- Feeling of “fullness”
- Fluid collection in abdomen
Diagnosis of mesothelioma will first determine the location and size of tumor formation using imaging studies, blood tests and patient history. Once diagnosis is made, a biopsy will likely be performed to remove a small portion of the tumor tissue.
This tissue will be examined by a pathologist under microscopic magnification in a process known as immunohistochemistry. This procedure will confirm that the cells are malignant and will identify the cells as coming from epithelial tissue to form epithelioid mesothelioma. It will also ensure that an accurate diagnosis is made as some epithelioid mesothelioma cells are very similar in appearance to other cancer cells such as adenocarcinoma.
Subtypes of Epithelioid Mesothelioma
Though epithelial cells are similar in appearance to one another and all function as protective layers, there are subtypes of epithelioid cells. Each subtype may be of a different size, shape, or structure and may react differently to particular treatments. Identification of a particular subtype may help to determine what treatments may be more successful. There are 20 different subtypes which include:
- Adenoid cystic
- Bakery Roll
- Clear Cell
- Gaucher Cell-like
- In Situ
- Mucin Positive
- Papillary or Well-differentiated Papillary
- Poorly Differentiated
- Single File
- Small Cell
Determining the epithelioid cellular sub-type will be done by a pathologist under microscopic examination. Differentiation between cells that may look similar to other types of cancer cells is critical for mesothelioma treatment.
One study has shown that certain sub-types, have a better prognosis than others and identification of each particular sub-type may help to determine what type of epithelioid mesothelioma treatment is likely to be most successful.
Treatment for mesothelioma is largely based on the type and location of the cancer, not the cell type. Epithelioid mesothelioma treatment is generally the same as for other cellular types but in many cases, treatment for epithelioid mesothelioma may be more successful than for mesothelioma caused by other cellular types. Because of this, some patients may wish to undergo aggressive treatments as they are more likely to have a good prognosis.
In general, those with epithelioid mesothelioma have a life-expectancy that is about 12 months. This is nearly twice that of other cell-types but with early diagnosis and appropriate treatment, may be extended to years in some patients.
Pleural mesothelioma with epithelioid cells can be treated with chemotherapy, radiotherapy, surgery or a combination of two or more treatment methods. As epithelial cells “stick” together and though they are likely to divide faster, growing larger tumors more quickly, epithelioid mesothelioma may have a better prognosis than other types of the cancer. Multimodal treatment including extrapleural pneumonectomy (removal of the lung), radiation and chemotherapy has been shown to dramatically increase the survival rate of certain epithelial cell-type, pleural mesothelioma treatments.
Peritoneal mesothelioma with epithelioid cell-type is rarer than the pleural disease but with aggressive treatment including chemotherapy, radiation and cytoreductive surgery, life expectancy may be increased. In addition, newer treatment methods such as immunotherapy, photodynamic therapy and targeted chemotherapy may help to improve the prognosis.
Treatment options and prognosis are determined by the combination of mesothelioma type, tumor location, staging, cell type and patient medical condition. As the cancer is rare and highly complex, it is essential that patients diagnosed with mesothelioma seek treatment from a physician who is a mesothelioma expert.