Small Cell Mesothelioma
One of the rarer cell types seen in cases of mesothelioma is small cell. The name describes the appearance of the cells under a microscope. The few cases of this type of mesothelioma are often categorized as epithelial, but some small cell tumors include sarcomatoid and other types of cells. Mesothelioma cases diagnosed as small cell have tumors with about half small cells.
Small cell mesothelioma may be misdiagnosed as small cell lung cancer, but studies of a few case studies have found significant differences between the two. As with most types of mesothelioma, the prognosis for the small cell type is not usually good and treatment most often cannot cure it. Treatments like surgery, chemotherapy, and radiation can be used to extend a patient’s life or to improve the quality of life.
Characteristics of Small Cell Mesothelioma
The cells that make up small cell mesothelioma are often a mix of types, but about half of them are described as small cell. These cells are small, uniform, and round, and contain a single large nucleus. Cases of small cell mesothelioma tumors have been described in the pleura of patients or the peritoneum. Most patients had a history of asbestos exposure. Small studies of a few cases of small cell mesothelioma have found that the additional cells in the tumors are usually mostly epithelial, but may also be a biphasic mix of epithelial and sarcomatoid.
Small Cell Mesothelioma vs. Small Cell Lung Cancer
Mesothelioma and lung cancer are often difficult to distinguish when making a diagnosis. Lung cancer and pleural mesothelioma occur very close to each other in the body and their cell structures when examined under a microscope by a pathologist often look very similar. Both types of cancer can form in a small cell variety, both less common than other types.
One study investigated 13 cases of small cell mesothelioma to determine what features distinguished them from small cell lung cancer. These features can be used to make a more accurate diagnosis. The study found that small cell mesothelioma tumors lacked certain patterns of cell growth seen in small cell lung cancer: rosettes, ribbons, and streams. The study also found unique characteristics in the nuclei of the mesothelioma cells. Using immunohistochemistry and markers in tumors the study found two markers that were not present in any of the 13 tumors. This fact could also be used to diagnose small cell mesothelioma.
Diagnosis and Immunohistochemistry
Diagnosing mesothelioma is already difficult, but when the characteristics of the tumor cells include those of small cell, it can be even more of a challenge. It may be a long journey from first symptoms to a diagnosis of small cell mesothelioma, but it begins with a physical examination and imaging scans. For respiratory and chest symptoms an X-ray can rule out things like pneumonia. More detailed scans of the abdomen or chest can show that here are tumors or areas of tissue that look abnormal and may be cancerous.
These imaging scans lead to biopsies, samples of tissue and fluid that are removed from the suspected tumors and examined by pathologists. By looking at cells under a microscope a pathologist will try to determine if they are malignant, if they originated in the mesothelium, if they are sarcomatoid or epithelial cells—or a mixture of both—and finally if there are any signs of cellular subtypes, like small cells.
To identify a small cell tumor, pathologists look for round, uniform, small cells. In one study of eight cases of small cell mesothelioma, between 80 and 100 percent of the cells in the biopsy samples appeared to be small cells. The proportion of small cells to other types can vary, but when the majority have small cell characteristics, the diagnosis is likely to be small cell mesothelioma.
Looking at the physical appearance and growth patterns of the tumor cells is not always enough to diagnose a certain type of mesothelioma accurately. The few studies that have investigated these tumors found that a more accurate diagnosis includes both pathological study of cells and immunohistochemical staining. The latter uses immune system proteins as markers. There are certain proteins that have found to be present in most or all cases of small cell mesothelioma and others that have never been found. These details help make a better diagnosis.
Getting an accurate diagnosis is crucial for treating any type of cancer, especially one that is as difficult to treat as mesothelioma. For small cell mesothelioma, as with other types, the treatment plan varies by individual and depends on the stage of the cancer. The later the stage is, the more difficult it is to treat and the less likely it is that surgery will be an option.
Because it has a long latency period anyway and because small cell mesothelioma is difficult to diagnose, many of the few cases of this illness are only diagnosed at a later stage, leaving surgery out as an option for treatment. That leaves chemotherapy and radiation, although these are unlikely to cure the cancer.
These strategies for treatment can be used to reduce the sizes of tumors with the hope that doing so will extend the patient’s life. These treatments can also be used to reduce symptoms and to make the patient feel more comfortable with the time he or she has remaining.
In one study of eight patients with small cell mesothelioma, the average survival time was just over eight months. With so few cases to study it is impossible to give a prognosis that is accurate. What the experts know, however, is that mesothelioma almost never comes with a good prognosis.
From what is known about small cell mesothelioma, it does seem that it is very aggressive and that life expectancy for it is not long. Treatments are mostly used to give a patient some more time and as palliative care. If you have been diagnosed with any type of mesothelioma, make sure you know your rights with respect to asbestos exposure and the law.
Page edited by Dave Foster
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