In histological terms, there are four different types of mesothelioma: sarcomatoid, epithelial, biphasic, and desmoplastic (a variant of sarcomatoid).In medical terms, the term histopathology refers to the microscopic examination of cellular tissue to gain insight into the manifestations of various diseases.



Malignant sarcomatoid mesothelioma is the least common of the four cellular types. It accounts for approximately 7 to 20 percent of cases. When viewed under a microscope,the malignant cells appear as elongated spindle-shaped cells that are irregularly shaped and often overlap one another.

Desmoplastic mesothelioma is considered a variant of sarcomatoid mesothelioma. This form is likely the most difficult of all mesotheliomas to diagnose. When desmoplastic mesothelioma invades or metastasizes, the cells can appear very bland and can be misdiagnosed as benign fibrous tissue. Medical experts say this form should not be diagnosed with a needle core biopsy.

It's important to know that malignant sarcomatoid mesothelioma is sometimes difficult to diagnose on the basis of histological methods. For example, cells of another type of cancer called pulmonary sarcomatoid carcinoma are very similar in appearance (as well as other characteristics) to malignant sarcomatoid mesothelioma.

For this reason, if you are diagnosed with cancer and you know that you have been exposed to asbestos at some time in the past, obtaining a second diagnostic opinion may be important. Different types of cancer vary widely in terms of prognosis and treatment options, and if misdiagnosed, patients may not receive the most appropriate treatment for their cancer.

Treatment and Prognosis

Each of the four cellular forms of mesothelioma is generally treated in the same way. Treatment is not based on the specific type of cells involved, but instead on the location of tumors and the stage of the cancer.

Each type of cancer responds to treatment very differently. In general, patients with malignant sarcomatoid mesothelioma have a poorer prognosis than patients with the epithelioid type , as sarcomatoid cancers are more aggressive and more resistant to treatment. Unfortunately, the general prognosis for all the different types is usually poor, and the difference in prognosis between sarcomatoid, epithelioid, biphasic and desmoplastic cancers may amount to as little as a few months.

Biopsy and Histopathology

Patients undergoing medical evaluation to ascertain a diagnosis of mesothelioma will also have to undergo a variety of medical tests to determine the location and nature of the cancer.

- Biopsy: This involves removal of samples of suspected cancer cells from several locations in the tumor site which are taken to the laboratory for proper evaluation to determine what type of cells they are and whether the cells are malignant.

The biopsy samples are tested in the laboratory under the principles of histopathology in two ways:

- They are viewed under a microscope to determine their general appearance.

- The cells are also tested for the presence of oncoproteins and molecules that are specific to certain type of cancer cells.

When viewed under a microscope, mesothelioma cells and other types of cancer cells have different types of appearance and different shapes when compared to normal healthy cells. Further tests that evaluate the types of proteins present on the surface of the cells are needed to determine the exact nature of the cells.

When mesothelial cells become malignant, they begin to produce different types of proteins and some of these are present on the surface of the cells. Examining the types of surface proteins allows a histologist to determine if the cells are malignant mesothelioma, another type of cancer, or healthy cells. The application of histochemistry in the diagnosis of mesotheliomas is primarily to differentiate epithelial mesotheliomas from mucin-producing adenocarcinoma.