Rare Subtypes of Epithelial Mesothelioma

Mesothelioma is a rare type of malignant cancer that is aggressive and difficult to treat. It is most often associated with asbestos exposure, although some people who develop it were never around the harmful material. Mesothelioma can be categorized by where in the body it develops first but also by cell type involved and cell subtypes.

Epithelial mesothelioma is one kind of the cancer based on cell type. It is the more common type and can be subdivided by shape and growth pattern of cells. There are multiple subtypes of epithelial mesothelioma, but many of these are rare and have been seen in only a small number of patients. Because of their rarity, information about these subtypes is limited.

Epithelial Mesothelioma

By using cell type, mesothelioma can be grouped into three broad categories. The most common is epithelial, cancer that impacts epithelial cells. Less common is mesothelioma of sarcomatoid cells. The third group is called biphasic, mesothelioma in which the cells involved include a mix of both epithelial and sarcomatoid.

Epithelial cells exist all over the body and make up tissue that provides a protective barrier in the skin, around organs, in the throat, and in other areas. These cells are normally healthy, but they can become cancerous under certain circumstances, such as after exposure to asbestos. Mesothelioma of epithelial cells can occur in the pleura around the lungs and in the peritoneum in the abdominal cavity.

Epithelial mesothelioma is distinguished from sarcomatoid mesothelioma by cell type but also by prognosis. The growth and spread of cancerous epithelial cells occurs more slowly than with sarcomatoid mesothelioma, a more aggressive cancer. 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 sizes, shapes, growth patterns, and other characteristics in epithelial cells, including those that become cancerous during the development of mesothelioma. When diagnosing mesothelioma, pathologists study tissue samples under a microscope and describe the cell patterns to identify a subtype. There are several epithelial subtypes that have been recorded in case studies but that are not very common.

• Clear cell. This is a very rare type of mesothelioma in which the cytoplasm, or interior, of the cells appear clear when viewed under magnification. It is difficult to diagnose because it is rare and because there are more common carcinomas of renal cells, lung cells, skin cells, and others. If clear cancer cells are found in the pleura or peritoneum it must be determined if they are mesothelioma cells or cells that metastasized from other locations in the body.
• 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 as a way to distinguish between mesothelioma and adenocarcinoma, but it has now been recorded that mesothelioma cells may rarely contain mucin.
• Adenoid cystic. Also rare is an adenoid cystic pattern of epithelial cells in mesothelioma. 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 the presence of a large vacuole, a space or cavity within the cell. This makes the cell appear as if it is a ring 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 been recorded but may only ever have 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 is crucially important when there are rare subtypes of this kind of mesothelioma. The biggest risk is that it will be mistaken for another type of cancer, like adenocarcinoma, which would require a different treatment plan for the best outcomes. Pathologists must look very carefully at biopsy samples from the patient to determine not just the shape and pattern of the cancer cells but also from what tissue or part of the body they originated.

Treatment for any subtype of epithelial mesothelioma depends very much on the individual patient and how far the cancer has progressed. Surgery is often used if the cancer has not spread too far or become too diffuse. This helps to remove as much of the cancerous tissue as possible and can be followed by radiation therapy or chemotherapy to destroy any remaining cells if possible.

With rare types of mesothelioma, delayed diagnosis or an incorrect diagnosis is common. This is because it is difficult to distinguish between these rare mesotheliomas and similar cell patterns in more common types of cancer. Many people with a rare type will be diagnosed once the cancer has already spread or metastasized. This makes treatment more difficult and the outcomes less positive.

For this reason it is crucial that you be diagnosed as early as possible if you have mesothelioma symptoms or know that you have been exposed to asbestos in the past. The sooner you can get screened for cancer, the better your chances of getting the right diagnosis in time for treatment to be more effective.