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Mesothelioma is a rare cancer that is difficult to treat. This aggressive cancer is most often associated with asbestos exposure, although some people develop the disease without ever being near the harmful mineral. Mesothelioma is categorized by where it develops in the body as well as the cell type involved and cell subtypes.
Epithelial mesothelioma is one category of mesothelioma based on cell type. This is the most common subtype and can be subdivided by cell shape and growth pattern. While there are multiple subtypes of epithelial mesothelioma, many are incredibly rare with only a small number of diagnosed patients. Because of their rarity, information about these subtypes is limited.
By using cell type, mesothelioma can be grouped into three broad categories. The most common category is epithelial mesothelioma, so named because it impacts epithelial cells. Mesothelioma of sarcomatoid cells is less common. The third group is called biphasic mesothelioma, which includes a mix of both epithelial and sarcomatoid cells.
Epithelial cells are the building blocks of tissue that provides a protective barrier in the skin, around organs, in the throat, and other areas. These cells are normally healthy. However, under certain circumstances, these cells can become cancerous. One such circumstance is exposure to asbestos. Mesothelioma of epithelial cells can occur in the pleura around the lungs and in the peritoneum in the abdominal cavity.
While epithelial mesothelioma is distinguished from sarcomatoid mesothelioma by cell type, it also differs in prognosis. The growth and spread of cancerous epithelial cells occurs more slowly than with sarcomatoid mesothelioma. Treatment can often be used more effectively in most types of epithelial mesothelioma resulting in greater survival rates and life expectancies.
Epithelial Subtypes of Mesothelioma
There can be a great variety of characteristics like sizes, shapes, growth patterns in epithelial cells. When diagnosing mesothelioma, pathologists study tissue samples under a microscope and use cell patterns to identify mesothelioma subtype. There are several epithelial subtypes recorded in case studies, although they are uncommon.
- Clear cell. This rare type of mesothelioma has clear cell cytoplasm. This clear cell interior can be seen when examined under a microscope. Because it is so rare, this type of mesothelioma is difficult to diagnose. If clear cancer cells are found in the pleura or peritoneum, doctors must determine if they are mesothelioma cells or cells that metastasized from other locations.
- Mucin-positive. This type of mesothelioma is extremely rare. It occurs when epithelial mesothelioma cells test positive for mucin, the protein that makes up mucous. A positive test for mucin was once used to distinguish between mesothelioma and adenocarcinoma. However, it has been recorded that mesothelioma cells may contain mucin although this is rare.
- Adenoid cystic. An adenoid cystic pattern of epithelial cells in mesothelioma is also rare. This structure includes a cribriform pattern, which means multiple small holes, tubular structures, and fibrous supporting tissue. This can easily be misdiagnosed as adenoid cystic carcinoma and adenocarcinoma.
- Signet ring. The rare signet ring form of epithelial mesothelioma cells are characterized by a large vacuole which is a cavity within the cell. This makes it look like there is a ring inside the cell with a large stone on one side. Signet ring mesothelioma must be differentiated from adenocarcinomas and carcinomas with the same structure.
- Other types. There are other subtypes of epithelial mesothelioma that are so rare they have only ever been observed in a handful of patients. These include glomeruloid, histiocytoid, bakery roll, gaucher-like, single file, macrocystic, microcystic, placentoid, and pleomorphic.
Diagnosing and Treating Rare Epithelial Mesotheliomas
Diagnosis of the subtype of mesothelioma is crucially important. It is important to make sure mesothelioma is not mistaken for another type of cancer, like adenocarcinoma, which would require a different treatment plan. Pathologists must carefully examine biopsy samples to determine not just the shape and pattern of the cancer cells, but also from what tissue they originated.
Treatment for any subtype of epithelial mesothelioma depends on the individual patient and how far the cancer has progressed. Surgery is often used if the cancer has not metastasized. Surgery removes as much cancerous tissue as possible and can be followed by radiation therapy or chemotherapy to destroy remaining cells.
With rare types of mesothelioma, delayed or incorrect diagnosis is common. This is because distinguishing between tare types of mesothelioma is difficult. Many people with a rare type will not be properly diagnosed until the cancer has already metastasized. A 61-year old female patient with clear cell mesothelioma that developed in the peritoneum died due to large amount of ascites and respiratory failure 11days after her admission to the hospital in Japan. Diagnosis happened after she died. Late diagnosis of the disease makes treatment difficult and leads to poor survival rates.
For this reason, early diagnosis is crucial. If you have any symptoms of mesothelioma or have been exposed to asbestos, regular screening will improve treatment options and possible outcomes.
Page Medically Reviewed and Edited by Pinar Kanlikilicer, PhD
Dr. Pinar Kanlikilicer has a PhD in Biomedical Engineering. She completed her 5-years of postdoctoral training in the Department of Experimental Therapeutics at MD Anderson Cancer Center. She is currently working in the field of cancer as a research scientist.