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Heterologous mesothelioma is a very rare subtype of this already rare type of cancer. Regardless of form—pleural, peritoneal, or pericardial—the general characteristics and symptoms of this subtype are the same as with other subtypes. What makes this cancer type unique is the characteristics of the cells that make up the mesothelioma tumors.

Heterologous refers to the fact that these tumors contain cells not just of the tissue of origin, in this case the mesothelium, but also other types of cells. Heterologous mesothelioma tumors may include bone cells and other kinds of cells. This type of mesothelioma is so rare that little is known about it. Only a handful of cases have been studied, but generally the symptoms, diagnosis, treatment, and prognosis are similar to other types of mesothelioma.

Case Studies of Heterologous Mesothelioma

The little information that is known about this type of mesothelioma come from studies of individuals found to have mesothelioma with tumors that have heterologous characteristics. In one study of 27 individuals, 89 percent had pleural mesothelioma and the remaining 11 percent were diagnosed with peritoneal mesothelioma. Only seven percent of the patients were women, and the median age was 68. Most of the patients were diagnosed with sarcomatoid or biphasic mesothelioma. Just one had epithelial mesothelioma.

The different types of tissue or cells found in the mesothelioma tumors of these cells included cartilage, bone cells, and muscle cells. The ratio and combination of types of cells present in the tumor varied by patient. Some had just one unusual cell type, while others had multiple. The survival rate was low among these patients, but consistent with any other subtype of sarcomatoid mesothelioma, the most aggressive form of mesothelioma.

What Causes Heterologous Mesothelioma?

Like other types of mesothelioma, this cell subtype is associated most strongly with asbestos exposure. Why cell types from other parts of the body end up in the mesothelioma tumor is not understood. Early studies suggest that it may be caused by a process called cellular differentiation. This is a normal process that allows cells to adapt and specialize in order to perform certain functions. Differentiated cells change to complete a job, but then typically are unable to divide. They simply die after completing the job.

Cellular differentiation in cancer cells and tumors is atypical. However, healthy mesothelium cells are known to be able to differentiate, including changing into connective tissue. This may explain what happens in people diagnosed with heterologous mesothelioma. The cancer cells, because they began in the mesothelium, are able to differentiate and change, although why they do so is not known.

Diagnosis and Treatment

The diagnosis and treatment of this very rare type of mesothelioma follows the same guidelines as other types. Diagnosis includes a physical examination of symptoms, an imaging scan, and a biopsy. The imaging scan usually finds that there is some abnormal type of tissue, but it is the biopsy that determines if it is cancer. A biopsy involves using a thin needle to extract a sample of tissue or fluid, or if the tumor is difficult to reach, more invasive surgery to remove a piece of tissue.

The tissue sample is investigated under a microscope by a pathologist. This expert looks at the cells to determine if they are malignant, if they originated in the mesothelium, and what subtype they are. For rare subtypes like heterologous mesothelioma, immunohistochemistry may be used to make a more accurate diagnosis. This technique can use specific antibodies, proteins, to detect antigens, another type of protein, on the cancer cells. This can help to pinpoint specific types of cells like bone cells and cartilage, within a mesothelioma tumor.

Because most described cases of heterologous mesothelioma have been sarcomatoid, treatment is difficult. This is the most aggressive type of mesothelioma and it typically spreads rapidly and is often already metastasized by the time a diagnosis is made. For sarcomatoid mesothelioma, surgery is not usually an option. Most patients will rely on chemotherapy, radiation, and other treatments to reduce pain and other symptoms. Treatment for this type is mostly palliative, and any hope of a cure is minimal.

Radiation and chemotherapy can be used to shrink tumors, which generally helps to make a patient more comfortable. Other treatments like medications for pain or draining fluid from around the lungs or in the abdomen can also help patients live more comfortably with the time they have left.

Prognosis

In the study of 27 patients diagnosed with heterologous mesothelioma the median survival time after diagnosis was only six months. It is a small group from which to base a general prognosis, but because the cases were almost all sarcomatoid or biphasic, it is accurate to assume that the prognosis for this rare subtype is poor. Treatment is likely to be used to relieve symptoms, although it may extend the life of a patient by just a little bit of time.

Although the prognosis is never very good, it is better for any type of mesothelioma when the diagnosis is made as early as possible. Anyone who has been exposed to asbestos, the number one cause and risk factor for mesothelioma, should be aware of the signs of this cancer and should be screened for it regularly. This gives patients the best possible prognosis and the best chance of receiving treatment that will make a difference.

If you were diagnosed with heterologous, or any type, of mesothelioma, you may have legal rights to seek compensation. Asbestos is the number one cause of this rare and aggressive type of cancer and chances are you were exposed at work without realizing the risks. Many people have suffered and died because of exposure to asbestos. Employers and manufacturers of asbestos-containing products can often be found to be to blame for this and lawsuits, settlements, and even trust funds have become available to help mesothelioma patients seek compensation. Let a lawyer guide your next steps and help you figure out how to get the compensation that will help you cover medical and other expenses.

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