Heterologous Mesothelioma
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Heterologous mesothelioma is a rare cell sub-type of mesothelioma, in which the tumor contains cells from other parts of the body, such as bone tissue.[1][2] Very few cases have been studied, but the symptoms, diagnosis, treatment, and prognosis are similar to other types of mesothelioma.
What Is Heterologous Mesothelioma?
There are three types of mesothelioma based on cell type:
Within these types, experts place subtypes, some of which are so rare experts only know of a few cases. Among these rare mesothelial cells is the heterologous type.
Heterologous can be any type, but it most often occurs in patients with the sarcomatoid cell type. Heterologous means that the tumors contain cells of other types of tissue, not just mesothelium cells. For instance, some heterologous mesothelioma tumors contain bone cells.
Facts About Heterologous Mesothelioma
Though information is scant, what we do know about heterologous mesothelioma comes from studies of individuals with tumors that have heterologous characteristics.[3] In one review of twenty-seven individuals:[4]
- Eight-nine percent had pleural mesothelioma
- The remaining 11% were diagnosed with peritoneal mesothelioma
- Only 7% of patients were women
- 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 the disease. Median survival for patients with heterologous mesothelioma was found to be six months after diagnosis.[4]
What Causes Heterologous Mesothelioma?
Like other types of mesothelioma, heterologous mesothelioma is associated with asbestos exposure.[4] 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. 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.
Diagnosing Heterologous Mesothelioma
Diagnosis and treatment of this very rare type of mesothelioma follow 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, pathologists may use immunohistochemistry 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.
How Is Heterologous Mesothelioma Treated?
Treatment of heterologous mesothelioma is difficult because most are sarcomatoid.[1] 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 feel more comfortable for their remaining time. These treatments include pain medication and draining fluid from around the lungs or in the abdomen.
Although surgery isn’t typically used for sarcomatoid types, a case study of a man with heterologous mesothelioma showed some positive results with trimodal therapy.
Doctors diagnosed the 69-year-old man with pleural heterologous mesothelioma. He underwent pneumonectomy surgery and received follow-up chemotherapy and intensity-modulated radiation therapy.
The man survived 12 months after trimodal therapy and still showed no recurrence in the chest cavity where surgeons removed tumors. Unfortunately, the cancer recurred in the peritoneum, leading to the man’s death.[5]
What Is the Prognosis?
Unfortunately, living 12 months after diagnosis and treatment is uncommon for most patients with sarcomatoid mesothelioma, the main cell type for heterologous tumors.
In one 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 palliative and used to relieve symptoms; although, it may extend the life of a patient for a short period.
Although the 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 asbestos exposure.
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.
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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.