Lymphohistiocytoid mesothelioma is one of the rarest of all variants of this type of cancer. Mesothelioma, the cancer of the tissue that lines organs throughout the body, is often categorized by cell type: epithelial, sarcomatoid, or biphasic. Lymphohistiocytoid is a very rare subtype of sarcomatoid mesothelioma, which is itself the rarest of the three cell types. Sarcomatoid mesotheliomas tend to be very aggressive.
Lymphohistiocytoid mesothelioma is cancer that is made up of a mixture of sarcomatoid cell types. It is often misdiagnosed, especially as lymphoma, because of the cell types found in the tumor. Already an aggressive and difficult to treat type of cancer, delayed diagnoses make lymphohistiocytoid even more difficult to treat and deadly, with survival rates for most patients measured only in a few months.
Cell Types in Lymphohistiocytoid Mesothelioma
This type of mesothelioma is considered a subtype of sarcomatoid mesothelioma. Sarcomatoid refers to the main type of cells in the tumors and they are cells made up of mesenchyme tissue. This kind of tissue makes up the structures of the lymphatic system, the circulatory system and some kinds of connective tissue, such as bone and cartilage. Only about 10 to 20 percent of mesothelioma cases are sarcomatoid, with the majority being made of epithelial cells.
Sarcomatoid cells are distinguished them from epithelial cells in mesothelioma tumors by certain characteristics of appearance and activity. Sarcomatoid cells in tumors shaped like spindles with elongated and large nuclei, sometimes even multiple nuclei. Sarcomatoid tumors are also distinguished from epithelial tumors by the fact that the cells spread and metastasize more rapidly and more aggressively. For this reason, all types of sarcomatoid mesothelioma are considered to be deadlier and less treatable than epithelial mesotheliomas.
What makes lymphohistiocytoid a unique subtype is the mix of cells within the tumor, which may even include some epithelial cells. These tumors have been found to include lymphocytes and histiocytes. A histiocyte is a kind of immune system cell that remains stationary as opposed to moving through the bloodstream. A lymphocyte is also an immune cell, a small type of white blood cell that is part of the lymphatic system, the network of vessels that carries lymph fluid from the lymph nodes to fight infections.
Diagnosis and Misdiagnosis
Very few cases of lymphohistiocytoid mesothelioma have ever been reported, but those few have been studied and published in the scientific literature. This helps to make diagnoses in the future, but for many people with this type of cancer, a misdiagnosis is likely. In fact, one thought as to why there are so few cases of lymphohistiocytoid mesothelioma is that it has too often been misdiagnosed, that there are more cases of it than the literature would suggest.
Any diagnosis of mesothelioma begins with a physical exam and imaging scans of the chest cavity and lungs, or in the case of peritoneal mesothelioma, of the abdomen. Imaging scans can help to pinpoint abnormal tissue that may be the result of tumors. To confirm that these are cancerous, and to determine which type and subtype, a biopsy must be done to remove a small sample of tissue and fluid.
This biopsy sample gives a pathologist cells from the tumor to investigate. By the appearance of the cells in the tumor a diagnosis can be made, but this is not a perfect way to figure out the type of cancer. Mesothelioma especially is difficult to diagnose this way. The cells can often look like the cells of other types of cancer, like lung cancer.
In the case of lymphohistiocytoid mesothelioma, the cells most often resemble those seen in lymphoma, the cancer of the lymphocytes of the lymphatic and immune system. Lymphoma is a common misdiagnosis for lymphohistiocytoid mesothelioma. In the few cases that have been reported, most of the patients were originally told they had lymphoma. Other misdiagnoses of lymphohistiocytoid mesothelioma that have been made include ganglioneuroma, an inflammatory pseudotumor, thymoma, and lymphoepithelial carcinoma.
Because of the mix of cells involved in lymphohistiocytoid mesothelioma, making an accurate diagnosis is difficult using standard pathological techniques. Research, however, has shown that immunohistochemistry, staining and using immune system markers, can distinguish this type of cancer from others. Immunohistochemistry uses antibodies, proteins of the immune system, to target and identify antigens, also proteins, that are specific to certain cells.
Researchers studying the diagnosis of lymphohistiocytoid mesothelioma in the few patients that were known to have it found that there are certain markers that are characteristic of this type of mesothelioma, particularly cytokeratin. One study found that the presence of this marker in immunohistochemical stains could rule out other cancers like lymphoma. Other markers that can help make a diagnosis are calretinin and vimentin.
Treatment and Prognosis
All types of mesothelioma are difficult to treat and most often have no hope of being cured. Sarcomatoid types of mesothelioma, which includes lymphohistiocytoid mesothelioma, are considered even more difficult to treat than epithelial types. This is because sarcomatoid cancer cells tend to adhere less well to each other and can therefore spread out from the original tumor earlier and more quickly.
Most sarcomatoid mesotheliomas are not considered to be treatable by surgery. That leaves chemotherapy and radiation therapy, which can act to shrink tumors, but are unlikely to eliminate them entirely. The treatment of lymphohistiocytoid mesothelioma using these methods is most often done to extend the lifespan of a patient and to relieve symptoms, like pain and difficulty breathing.
The prognosis for lymphohistiocytoid mesothelioma, like all types of mesothelioma is not usually positive. Most people are diagnosed after the disease has progressed and is very difficult to treat. This is especially the case with lymphohistiocytoid mesothelioma because it is so easy to misdiagnose. In one case study the three patients only lived four, five, and eight months after receiving the diagnosis. Unfortunately nearly all cases of mesothelioma end in taking a life early, which is why it is so important that anyone who was exposed to asbestos be screened early and often. The only way to cure this cancer is to prevent it or to catch it very early.
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