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Heterologous mesothelioma is a very rare sub-type of this already rare type of cancer. The general symptoms and characteristics of heterologous mesothelioma are the same as other sub-types. However, makes this cancer type unique is the characteristics of the tumor cells.
Heterologous literally means “consisting of differing elements.” In heterologous mesothelioma, tumor cells contain from other parts of the body. Heterologous mesothelioma tumors may include bone cells and other kinds of cells. Because this type of mesothelioma is so rare, very little is known about it. Generally the symptoms, diagnosis, treatment, and prognosis are similar to other types of mesothelioma even though very few cases have been studied.
Case Studies of Heterologous Mesothelioma
Though information is scant, what we do know about heterologous mesothelioma come from studies of individuals with tumors that have heterologous characteristics. In one study of 27 individuals, 89 percent had pleural mesothelioma. The remaining 11 percent were diagnosed with peritoneal mesothelioma. Only seven percent of patients were women and the median age was 68. Most patients were diagnosed with sarcomatoid or biphasic mesothelioma. Just one had epithelial mesothelioma
Cell types found in heterologous mesothelioma tumors included cartilage, bone cells, and muscle cells. The ratio and combination of cell types 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 other sub-types of sarcomatoid mesothelioma, the most aggressive form of mesothelioma. Median survival for patients with heterologous mesothelioma was found to be 6 months after diagnosis.
What Causes Heterologous Mesothelioma?
Like other types of mesothelioma, heterologous mesothelioma is associated with asbestos exposure. Why cell types from other parts of the body end up in these tumors is not understood. Early studies suggest it may be caused by a process called cellular differentiation. Cellular differentiation is a normal process that allows cells to adapt and specialize to perform certain functions. Differentiated cells change to complete a job. However, after morphing they are typically unable to divide. Instead, they simply die after completing the job.
Cellular differentiation in cancer cells and tumors is atypical. However, healthy mesothelium cells are known to have the capacity to differentiate, sometimes changing into connective tissue. This may explain what happens in people diagnosed with heterologous mesothelioma.
Diagnosis and Treatment
Diagnosis and treatment of this very rare type of mesothelioma follows the same guidelines as other types. Proper diagnosis includes a physical examination of symptoms, an imaging scan, and a biopsy. The imaging scan usually finds some abnormal tissue types. Then a biopsy will determine if it is cancerous.
During a biopsy, a thin needle is used to extract a sample of tissue or fluid. If the tumor is difficult to reach, surgery may be required to obtain a sample. A pathologist then examines the sample under a microscope. By examining the cells, he or she can determine if they are malignant, what sub-type they are, and if they originated in the mesothelium. For rare sub-types, immunohistochemistry may be used for a more accurate diagnosis. This technique uses specific antibodies to detect antigens on the cancer cells. This can help pinpoint specific types of cells, like bone cells and cartilage, within a mesothelioma tumor. IHC staining of various cytokeratins, calretinin and desmin are performed in patients with heterologous mesothelioma tumors
Treatment of heterologous mesothelioma is difficult because most are sarcomatoid. By the time of diagnosis, this aggressive type of mesothelioma has often metastasized, continuing to spread rapidly through the body. Surgery is not usually an option for sarcomatoid mesothelioma. Most patients will rely on chemotherapy, radiation, and other treatments to reduce pain and other symptoms. Treatment for this type is mostly palliative.
Generally, radiation and chemotherapy are used to shrink tumors, helping the patient feel more comfortable. Other treatments may also help patients for more comfortable for their remaining time. These treatments include pain medication and draining fluid from around the lungs or in the abdomen.
In the study of patients diagnosed with heterologous mesothelioma, the median survival time after diagnosis was only six months. While this is a small group on which to base prognosis, it is safe to assume that the prognosis for this rare sub-type is poor. Treatment is generally used to relieve symptoms, although it may extend the life of a patient by for a short period of time.
Although general prognosis is poor, it can be slightly better when the diagnosis is made early. Asbestos exposure is the number one risk factor for developing mesothelioma. For this reason, anyone who has been exposed should be aware of the signs and receive regular screening. This gives patients the best chance of receiving treatment that will make a difference.
If you were diagnosed with heterologous mesothelioma, you may have legal rights to seek compensation. Because asbestos is the leading cause of this rare cancer, you may have been exposed without realizing the risks. Many people have suffered and died because of exposure to asbestos. Employers and manufacturers of asbestos-containing products are often to blame. Lawsuits, settlements, and trust funds are available to help mesothelioma patients seek compensation. Let a lawyer help you determine how to get the compensation to help cover medical and other expenses.
Page Medically Reviewed and Edited by Pinar Kanlikilicer, PhD
Dr. Pinar Kanlikilicer has a PhD in Biomedical Engineering. She completed her 5-years of postdoctoral training in the Department of Experimental Therapeutics at MD Anderson Cancer Center. She is currently working in the field of cancer as a research scientist.