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Lymphohistiocytoid mesothelioma is one of the rarest subtypes of this already rare cancer; sarcomatoid mesothelioma. Mesothelioma is a cancer of the tissue that lines organs throughout the body and is often categorized by cell type. Types include epithelial, sarcomatoid, or biphasic. Lymphohistiocytoid is a very rare subtype of sarcomatoid mesothelioma. Sarcomatoid mesotheliomas are typically extremely aggressive.
Lymphohistiocytoid mesothelioma cancer is a mixture of sarcomatoid cell types. Because of the types of cells in the tumors, it is often misdiagnosed, especially as lymphoma. An aggressive and difficult cancer to treat, lymphohistiocytoid mesothelioma becomes even deadlier when the diagnosis is delayed. Most patients can expect to live only a few months.
Cell Types in Lymphohistiocytoid Mesothelioma
Lymphohistiocytoid mesothelioma is a subtype of sarcomatoid mesothelioma. Sarcomatoid refers to the specific tumor cells, which are made up of mesenchyme tissue. This tissue makes up the lymphatic system, the circulatory system, and connective tissues like bone and cartilage. Only about 10 to 20 percent of mesothelioma cases are sarcomatoid. The majority are made of epithelial cells
Sarcomatoid cells are distinguished from epithelial cells in mesothelioma tumors by their appearance and activity. Sarcomatoid cells are shaped like spindles with elongated and large nuclei, sometimes even multiple nuclei. These tumors are also distinguished from epithelial tumors by their rapid growth and metastasis. All sarcomatoid mesotheliomas are deadlier and tougher to treat than epithelial mesotheliomas.
The mix of cells in the tumor makes lymphohistiocytoid a unique subtype. Some cells may be epithelial cells. These tumors sometimes include lymphocytes and histiocytes. A histiocyte is an immune cell that remains stationary rather than moving through the bloodstream. A lymphocyte is also an immune cell. Lymphocytes are small white blood cells that are part of the lymphatic system, the network of vessels carrying lymph from lymph nodes to fight infections.
Diagnosis and Misdiagnosis
Very few cases of lymphohistiocytoid mesothelioma have ever been reported. However, those few cases have been studied and described in scientific journals. This improves future diagnoses, but for many people with this rare cancer, a misdiagnosis is still probable. In fact, misdiagnosis may be the reason there are so few reported cases to begin with.
Any mesothelioma diagnosis begins with a physical exam and imaging scans of the chest cavity and lungs. In the case of peritoneal mesothelioma, imaging scans will be taken of the abdomen. Imaging scans can pinpoint abnormal tissue that may be the result of tumors. Afterward, a biopsy will probably be performed. For a biopsy, a tiny sample of tissue or fluid is removed from a tumor. This sample is then examined to confirm cancer and determine the type and subtype.
The diagnosis is based on the appearance of the tumor cells. However, this is not the best way to determine the type of cancer. Mesothelioma is particularly difficult to diagnose in this manner because its cells often look like many other cancer cells, including lung cancer.
For lymphohistiocytoid mesothelioma, 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 reported cases of lymphohistiocytoid mesothelioma, most patients were first told they had lymphoma. Other misdiagnoses of lymphohistiocytoid mesothelioma include ganglioneuroma, an inflammatory pseudotumor, thymoma, and lymphoepithelial carcinoma.
Because of the mix of cells involved in lymphohistiocytoid mesothelioma, accurate diagnosis with standard techniques is difficult. However, research shows that immunohistochemistry staining and using immune system markers can distinguish this type of cancer. Immunohistochemistry uses antibodies to target and identify antigens specific to certain cells.
Researchers studying the diagnosis of lymphohistiocytoid mesothelioma in the few patients known to have it found certain markers characteristic of this type of mesothelioma, particularly cytokeratin. One study found the presence of this marker in immunohistochemical stains could rule out other cancers like lymphoma. Other markers that can help in diagnosis are calretinin and vimentin. Recent studies suggest that BAP1 is a key marker to differentiating lymphohistiocytoid mesothelioma from other diseases, specifically from reactive mesothelial cell proliferation.
Treatment and Prognosis
All types of mesothelioma are difficult to treat and most cannot be 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 adhere weakly to each other, allowing them to spread earlier and more quickly.
Most sarcomatoid mesotheliomas cannot be treated by surgery. This limits options to chemotherapy and radiation therapy, which can shrink tumors, but are unlikely to eliminate them. The treatment of lymphohistiocytoid mesothelioma using these methods is most often lengthens a patient’s life and relieves symptoms like pain and difficulty breathing.
The prognosis for lymphohistiocytoid mesothelioma is rarely positive. Most people are diagnosed after the disease has progressed and it has become difficult to treat. Because lymphohistiocytoid mesothelioma is so easy to misdiagnose, proper diagnosis for this rare mesothelioma generally comes too late. In one case study, three patients only lived four, five, and eight months after diagnosis. Almost all cases of mesothelioma end a life early. This is why it is important that anyone who was exposed to asbestos be screened early and often. The only way to cure this cancer is to catch it very early.
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.