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Malignant mesothelioma is generally divided into three histological categories, or types of cells: epithelioid, sarcomatoid and biphasic mesothelioma. Within each of these mesothelioma cancer cell types, subtypes exist. Many mesothelioma patients display more than one cell type.
The diagnosis of mesothelioma cannot be specifically by lung x-rays or other types of imaging, because many different types of cancer can be present in the lungs. The images show only that a tumor may be present, but does not provide an indication of whether the tumor is mesothelioma. A biopsy must be performed where the mesothelioma cancer cell types are used to distinguish mesothelioma from other types of cancer, such as lung cancer.
Epithelioid Mesothelioma Cancer.
Epithelioid mesothelioma is the most common cell type, constituting approximately 50% to 70% of all malignant mesothelioma. These cells are relatively uniform in shape and have a tubular pattern with a distinct cell nucleus. The individual cells are shaped like cubes or multi-sided boxes.
Because of the similarity between adenocarcinoma and mesothelioma cancer cells, they are often confused and mesothelioma can be misdiagnosed. Inspection of the cancer cells under high-powered microscopes and identification of unique characteristics of the chemical properties of the cells can help make the proper diagnosis.
Epithelioid mesothelioma is the most common form of mesothelioma and accounts for 50 to 70percent of mesothelioma cancer cells. The individual cells are relatively uniform in shape with a unique tubular pattern and a cell nucleus that, when viewed under high magnification, is visibly distinguishable from other cell nuclei. However, other types of cancer can take a similar form, and if these cancers appear in the mesothelium, they can be confused with epithelioid mesothelioma. Adenocarcinoma is a type of cancer often confused with epithelioid mesothelioma.
Epithelioid Mesothelioma Versus Adenocarcinoma
Mesothelioma, including epithelioid mesothelioma, is a type of cancer that occurs in the mesothelium, which is an epithelium (protective layer of tissue) that surrounds certain organs. Epithelia, which are found throughout the body, exist to separate different bodily environments. For example, epithelial cells are found in the skin, which separates the outside of the body from the inside of the body. Depending on the location, an epithelium can serve many functions, including protection, absorption, filtration, excretion, secretion or sensory reception.
Adenocarcinoma is another type of cancer that can be found in the mesothelium. However, unlike epithelioid mesothelioma, adenocarcinoma does not originate in the mesothelium, but rather in the lining or inner epithelium of an organ. When an adenocarcinoma occurs in the lining of the lungs it can spread to the mesothelium, or pleura, surrounding the lungs. Since epithelioid mesothelioma can also appear in the pleura, it can be easily confused with adenocarcinoma.
Furthermore, since both epithelioid mesothelioma and adenocarcinoma derive from epithelial tissue, they have a similar cellular appearance. Although research does show that the tumor cells in epithelioid mesothelioma are usually more regularly uniform, cube-shaped and spread out than the tumor cells in adenocarcinoma, (which are more columnar and crowded) this distinction is difficult to make on a case-by-case basis. To add to this confusion, chemical staining of epithelioid mesothelioma and adenocarcinoma cancer cells sometimes shows similar results.
The clinical signs for adenocarcinoma of the lung and malignan mesothelioma are also similar. The symptoms of these diseases, both of which typically affect the older population, include chest pain, pleural effusions (fluid build-up) and respiratory difficulty. This is why cancer of the mesothelium, or epithelioid mesothelioma, and cancer of the lung epithelium, adenocarcinoma, are often mistaken and can be misdiagnosed.
If you or a loved one has had asbestos exposure and received a diagnosis of adenocarcinoma, it may be worthwhile to seek a second diagnostic evaluation, either by the same physician or an oncology specialist who has experience in mesothelioma cases.
Sarcomatoid Mesothelioma Cancer.
Sarcomatoid mesothelioma is the least common type of mesothelioma cancer cell and accounts for approximately 10% to 15% of malignant mesothelioma. These cells typically have more of an oval, irregular shape and the nucleus of each cell is not as visible with a microscope as the epithelioid mesothelioma cancer cells. Because of the similarity of appearance, the sarcomatoid cancer cells can also easily be confused with the more typical sarcoma cancer cells.
Sarcomatoid mesothelioma accounts for only about 10 to 15 percent of the mesothelioma cancer cells and it is the least common form of mesothelioma. Sarcomatoid cells are typically oval shaped, but more irregular. The nucleus of sarcomatoid cells is not as clearly visible under an electron microscope as the nuclei of epithelioid mesothelioma cancer cells. Because the irregular oval shape is a common among cancer cells, sarcomatoid mesothelioma can be confused with sarcomatoid carcinoma and with sarcoma.
Sarcomatoid Mesothelioma Versus Sarcomatoid Carcinoma.
Sarcomatoid mesothelioma is often confused with a wide variety of other types of cancer because of the sarcomatoid appearance, including sarcomatoid carcinoma. Although sarcomatoid cancer appears in other parts of the body, such as the kidney, it is relatively rare in the lungs. No more than 1.3percent of lung carcinomas are of the sarcomatoid type.
Pulmonary sarcomatoid carcinoma is the type most often confused with sarcomatoid mesothelioma. Similar to sarcomatoid mesothelioma, sarcomatoid carcinomas of the lung are much more common in men (four times more likely than in women) and there is a strong association with smoking. Pulmonary sarcomatoid carcinoma and sarcomatoid mesothelioma also share certain symptoms, such as chest pain, pleural effusions and respiratory difficulty.
Sarcomatoid Mesothelioma Versus Sarcoma.
Sarcomatoid mesothelioma also can be confused with high-grade sarcoma. While carcinoma affects the epithelium, sarcoma arises in the supportive tissue (bone, cartilage, fat or muscle). If the sarcoma spreads to the pleural surface, it can be difficult to differentiate from sarcomatoid mesothelioma.
Sarcoma cells and sarcomatoid mesothelioma cells can have a similar appearance under an electron microscope, and the staining of the tumor cells can provide similar results. In these cases, the pathologist must be careful to compare the appearance and staining of the cells, along with the overall appearance (localized versus diffuse pleural-based mass) and regularity of the tumor, when making a definitive diagnosis of malignant mesothelioma.
If you or a loved one has been diagnosed with high-grade sarcoma of the lungs or pulmonary sarcomatoid carcinoma and you have had previous asbestos exposure, it may be best to seek a second thorough examination from your current physician or from an oncologist who specializes in mesothelioma.
Biphasic Mesothelioma Cancer.
Approximately 20% to 40% of the mesothelioma cancer cells fall into the biphasic category, which is combination of the sarcomatoid and epithelioid types. The biphasic type can occur with the two types of cells intermixed continuously throughout the tumor, or with them in specific groupings. Transitional areas between the two cell types are often present.
Biphasic mesothelioma cancer cases have seen an increase in occurrence over the years. Whereas biphasic cancer was once seen in approximately 25 percent of all mesothelioma cases, it has recently appeared in approximately 46percent to 63percent of all cases.
Biphasic Mesothelioma Cancer:
A Mixture of Epithelioid and Sarcomatoid Cancer Cells.
Biphasic mesothelioma cancer differs from epithelioid and sarcomatoid mesothelioma cancer in that it does not have a unique cellular structure; rather, biphasic mesothelioma cancer is a mixture of epithelioid and sarcomatoid mesothelioma cancer subtypes. Epithelioid mesothelioma cancer cells are typically cube shaped, but columnar and flattened cellular types are occasionally seen too. Sarcomatoid, or fibrous, mesothelioma cancer cells are spindle-shaped or oval. Because biphasic mesothelioma cancer patients have two very different mesothelioma cell types associated with their disease, it can be an easier form of cancer to diagnose than either sarcomatoid or epithelioid (two cellular types that can be confused with a variety of other cancers).
Biphasic mesothelioma cancer typically produces a combination of epithelioid and sarcomatoid cancer cells as opposed to a mixture, meaning that the two subtypes occur in different parts of the tumor. In this sense, classifying a case of mesothelioma as biphasic is simply stating that the patient has both epithelioid and sarcomatoid mesothelioma cancer. When epithelioid and sarcomatoid cancer cells are separated throughout various parts of the tumor, it can lead to a misdiagnosis of the mesothelioma's subtype.
Evaluation of Biphasic Mesothelioma Cancer Tumors.
Histopathological examination of a section of the tumor (examination of the tissue) may uncover only epithelioid or only sarcomatoid cancer cells. By taking multiple sections of diseased tissue for examination, histopathologists are more likely to be able to identify a case of biphasic mesothelioma cancer. (Histopathological advancements could be one possible explanation for the rise in biphasic mesothelioma cancer cases.) Misdiagnosis of a mesothelioma subtype is not a problem because there is no difference in treatment between the three.
Treating Biphasic Mesothelioma Cancer.
Treatment options available for biphasic mesothelioma cancer, sarcomatoid mesothelioma cancer and epithelioid mesothelioma cancer are the same. Aside from having different cellular appearances, the three mesothelioma subtypes also have differing average survival times. The mean survival time of biphasic mesothelioma cancer patients (six months) is the lowest of the three.
Although the methods of treating biphasic mesothelioma cancer do not differ from those of treating epithelioid cancer or sarcomatoid cancer, the shorter average post-diagnostic survival time of biphasic mesothelioma cancer patients makes radical or more experimental treatments a more appealing option than standard treatment modalities.
Prognosis Based on Cell Type
The mesothelioma cancer cell type does affect the prognosis. A study conducted on 167 patients showed that patients had the following mean survival times:
| epithelioid |
----- 8.5 months |
| sarcomatoid |
----- 7 months |
| biphasic |
----- 6 months |
Treatment options are very similar for patients with the different cell types.
