Cell Types of Mesothelioma

Pleural mesothelioma cancer is made up of one of three cellular patterns: epithelioid, sarcomatoid or biphasic. Determining the cell type is important because it can help a doctor better diagnose and treat the disease.

The cellular variations are the result of the genetic mutation of healthy cells caused by prolonged asbestos exposure. The cell type can help determine a patient’s prognosis and the available treatment options, since some types respond better to treatment than others.

Pleural mesothelioma forms in a layer of tissue called the epithelium, which lines hollow organs and body cavities. The cells in this layer are called epithelial cells when they are healthy. When they become cancerous, they can morph into epithelioid or sarcomatoid cells, or a combination of the two, known as biphasic mesothelioma.

Characteristic of Pleural Mesothelioma Cell Types

Each cell type has specific characteristics, but the differences are subtle and can complicate the diagnosing process. The main cellular patterns of pleural mesothelioma cells are:

  • Epithelioid cells appear square-shaped with visible nucleus, and they tend to lump together. They are the most common type of cancerous mesothelioma cell, accounting for 50 to 70 percent of all mesothelioma cancers. Because they are the most treatable cell type, patients with epithelial cells have the most favorable prognosis.
  • Sarcomatoid cells appear spindle-shaped with plump, elongated nucleus and generally overlap one another. This cellular pattern is seen in about 10 to 20 percent of all mesothelioma tumors. Because they are the most aggressive cells and can easily spread, there are fewer treatment options for patients with this cell type and a shorter life expectancy is common.
  • Biphasic cells The biphasic cellular pattern is a mixture of epithelial cells and sarcomatoid cells. Approximately 20 to 35 percent of all mesothelioma tumors consist of this mix of cells. Prognosis may vary depending on the mixture of cells, and is more favorable in cases that contain more epithelial cells than sarcomatoid cells. If the tumor contains mostly sarcomatoid cells the cancer is likely to spread quicker, which can limit treatment options.

Treatment Based on Cell Type

Identifying which cellular pattern is present can affect the type of treatment plan recommended because the cells respond differently to treatment. This is why histology, or the study of cell anatomy, plays a vital role in developing the most effective treatment plan for patients.

Of the mesothelioma cell types, epithelioid cells tend to respond best to treatment, which often leads to a better prognosis. Sarcomatoid cells, on the other hand, don’t respond as well to treatment, which can limit treatment options and lower survival rates. The prognosis for cases with biphasic cells varies based on the mix of epithelioid and sarcomatoid cells. The more epithelioid cells, the more likely the tumor is to respond to treatment.

The type of cell present in each case can account for up to a 200-day difference in life expectancy.

A team of mesothelioma specialists will determine the prognosis and the best course of treatment based on what cell type is present, location, stage of the cancer and overall health of the patient. A more aggressive treatment plan may be available for epithelioid cases.

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Histology of Pleural Mesothelioma

Histology is a branch of biology and medicine that involves the study of the microscopic anatomy of cells and tissues of plants and animals, which is important when diagnosing any type of cancer. When cells are recognized as cancerous, histopathology, a branch of histology, provides an even closer look into the diseased cells.

When diagnosing pleural mesothelioma, a team of oncologists, histopathologists and surgeons work in unison to ensure the most accurate diagnosis. The first step is to obtain tissue or fluid samples, called a biopsy, to study with a microscope.

Once tissue or fluid samples are removed, pathologists prepare the sample for observation by staining it with chemicals, which will allows them to determine the microscopic structures of the mesothelioma cells. The cells are closely examined to differentiate mesothelioma cells from cells of other cancers. Biopsy tests are the only tests that can conclusively diagnose cancer.

Studying the cells in the body can also help prevent misdiagnosis. For example, misdiagnosis of sarcomatoid cells can happen because these cells closely resemble other conditions, such as localized fibrous tumors, metastasized renal cell carcinoma, fibrosarcoma, fibrous pleurisy, malignant fibrous histiocytoma and pleural liposarcoma.

People with a history of asbestos exposure who have been diagnosed with adenocarcinoma, a cancer that develops in the glandular tissues of the body, should seek a second opinion to make sure the diagnosis is correct, because its cells are strikingly similar to pleural mesothelioma cells.

Other Ways to Study Cells

Other techniques to examine cells include in situ hybridization (ISH) and immunohistochemistry (IHC). In situ hybridization uses radioactive or fluorescent probes to combine DNA and RNA to further study a cell and detect any abnormalities.

Immunohistochemistry combines immunological, anatomical and biochemical techniques to determine microscopic cell components to help diagnose diseases. The foundation of this technique is identifying antibodies, which are proteins that target foreign objects in the body such as bacteria and viruses. Immunohistochemistry is frequently used to diagnose mesothelioma; however, a number of medical experts suggest that this technique should only be used alongside other pathology testing techniques.

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