Mesothelioma Cell Types
Page Medically Reviewed and Edited by Pinar Kanlikilicer, PhD This page has been fact checked by a PhD who specializes in cancer research. Sources of information are listed at the bottom of the article.
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Specialists categorize mesothelioma tumor cells as benign or malignant, epithelial, sarcomatoid, or biphasic, or one of several other less common cell variants.[1] Examination of the tumor cells, known as histology, can help doctors determine the type of cancer and what treatments will best help the mesothelioma patient.
Histology
Histology is the study of cells. Pathologists use histology to aid the diagnosis of cancers. For cancers like mesothelioma, examining the cells of a suspected tumor can tell a doctor if the patient has cancer and if it is malignant.
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In some cases, these cells can also help determine where cancer originated. Mesothelioma cells are notoriously difficult to diagnose. They don’t always look different from other cancer cells. For example, pleural mesothelioma cells are very similar to lung cancer cells in morphology.
A biopsy is necessary to determine cell type for mesothelioma. A doctor takes a sample of fluid or tissue from an area of the body thought to have a tumor. The tissue sample is prepared on a microscope slide and stained to reveal the individual cells. A pathologist then examines the cells and attempts to identify them for proper diagnosis.[2]
Immunohistochemistry, a branch of histology, uses antibodies to stain tissue and fluid samples. These antibodies attach to specific antigens or proteins on certain types of cancer cells.
A pathologist can target one particular cancer cell type using immunohistochemistry, either confirming cancer or ruling it out.[1] In addition, a pathologist can also tell you the degree of your tumor’s growth rate or angiogenesis – new blood vessel formation – based on the use of immunohistochemistry markers such as ki67 or CD31.
Benign and Malignant Cells
Unfortunately, mesothelioma cells are almost always malignant. Malignant means they are capable of growing and spreading to nearby tissues and other organs. If left untreated, malignant cells are always fatal.
On the other hand, benign tumor cells do not spread through the body; instead, they may grow into a tumor that becomes uncomfortable or causes symptoms.
Benign mesotheliomas are rare. Some cell types considered benign mesotheliomas include papillary and adenomatoid.
Epithelial Cells
When a pathologist studies cells from a person with mesothelioma, they look for the type of cell in the tumor. These cells may be epithelial, sarcomatoid, or both.
Epithelial cells are the most common type and are found in 70% of malignant mesothelioma tumors.[1] These cells have specific physical characteristics, like large nuclei and distinctive branching patterns, which are discernible under a microscope.
Epithelial cells typically respond well to treatment; therefore, an epithelial mesothelioma diagnosis is generally better news than the alternative. Because epithelial cells adhere to one another, they spread and metastasize less readily.
Sarcomatoid Cells
Compared to epithelial cells, sarcomatoid cells have a distinctive, elongated spindle shape that is easy to identify under a microscope. About 10 to 20% of mesotheliomas are diagnosed as sarcomatoid.[1]
Sarcomatoid cells are more likely to spread aggressively. Sarcomatoid mesothelioma resists treatment and often forms multiple nodules rather than one or more large tumors. The prognosis of the sarcomatoid type of cancer is worse than for epithelioid.
Biphasic Mesothelioma
If a mesothelioma tumor includes both sarcomatoid and epithelial cells, it is called biphasic.[1] Doctors will diagnose cancer as biphasic if at least 10% of its cells are one type, with the remaining cells falling into the other category.
In other words, a tumor comprised of 90% sarcomatoid cells and 10% epithelial would be considered biphasic cancer. About 25 to 30% of mesotheliomas are biphasic.
Rare Cell Variations
Diagnoses may also include cell variants. Variants are rare and present unique treatment challenges.
- Deciduoid mesothelioma is a variant with epithelial cells. Originally, this unusual variant cell was mostly found in cases of peritoneal mesothelioma in young women. Approximately twenty to thirty cases of deciduoid mesothelioma are reported each year.[3]
- Another variation is lymphohistiocytoid mesothelioma. This rare variant contains malignant inflammatory immune cells, including plasma cells, histiocytes, and lymphocytes. In addition, epithelial and sarcomatoid cells are present in the tumor. Less than 1% of pleural mesothelioma diagnoses are classified as lymphohistiocytoid.[4]
- Desmoplastic mesothelioma most often occurs in cases of peritoneal mesothelioma. This type of mesothelioma accounts for about 5% of all cases related to asbestos exposure. Desmoplastic mesothelioma occurs when the malignant tumor triggers the fibrous growth of connective tissue, like collagen. Since this is a sarcomatoid type of cancer, and the prognosis is almost always poor.[5]
- When at least half of the cells in desmoplastic mesothelioma are of the small cell type, oncologists call it small cell desmoplastic mesothelioma. Small cells are what they sound like. They are smaller cells as compared to other types of cancer cells. Under the microscope, small cells look round, bland, and uniform.
Implications for Treatment
Understanding mesothelioma cell types is important for proper treatment. Different cells and tumors require different treatment approaches. Understanding the basic cell type and any rare variations can help a medical team determine the best treatment for an individual patient.
If you have been diagnosed with mesothelioma, be sure that you receive all possible tests. This will result in a complete diagnosis as well as the most comprehensive treatment strategy.
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.