Lymphohistiocytoid mesothelioma is a rare subtype of pleural mesothelioma that makes up less than 1 percent of all mesothelioma cases, and all of the reported cases are linked to asbestos exposure. This type of mesothelioma was first described in 1988 and classified as a variant ofsarcomatoid mesothelioma. Tumors are made up of a dense bundle of inflammatory immune cells, including lymphocytes (a type of white blood cell), plasma cells and immobile immune cells called histiocytes. Also called macrophages, histiocytes ingest foreign substances to protect the body from infection.
Despite the fact that this subtype is classified under the aggressive sarcomatoid cell type, lymphohistiocytoid mesothelioma tumors tend to have a mix of epithelioid cells and inflammatory cells. Some patients diagnosed with this subtype of the disease may receive a prognosis that is similar to that of an epithelial cell diagnosis, which is more favorable.
One explanation for the small number of reported cases of this subtype is that it is often misdiagnosed as non-Hodgkin’s lymphoma or another condition. Studies show that symptomsand treatment options for lymphohistiocytoid mesothelioma are relatively similar to those of other pleural mesothelioma types. Its rarity leaves researchers few opportunities to study it, and there is little information for review. However, mesothelioma researchers and pathologists identified tumor characteristics that can aid in a more accurate diagnosis.
Diagnosing Lymphohistiocytoid Mesothelioma
After surgeons take a sample of the tumor during a biopsy, the tissue is sent to a lab for apathological study. Because of the large number of immune cells found in lymphohistiocytoid mesothelioma tumors, they are often mistaken for other cancers with similar cellular makeup: non-Hodgkin lymphoma, lymphoepithelial carcinoma, sarcomatoid carcinoma of the lung and ganglioneuroma (a tumor that forms in nerve fibers).
Common Differential Diagnoses of Lymphohistiocytoid Mesothelioma
- Non-Hodgkin lymphoma
- Hodgkin lymphoma
- Lymphoepithelial carcinoma
- Sarcomatoid carcinoma of the lung
- Ganglioneuroma
- Pleural-based thymic epithelial tumor
When doctors look at biopsied tissue under a microscope, histological studies reveal large, atypical polygonal to spindle-shaped histiocytoid cells. Mixed into these cells are white bloods cells (lymphocytes). Other signs of this tumor type are diffuse pleural thickening, small nodules throughout the pleura (the lining of the lung) and pleural effusion (a fluid buildup between pleural layers).
But for this type of mesothelioma, histological studies and visual presentation of pleural-tissue changes are not usually enough to make a firm diagnosis. For a definitive diagnosis of lymphohistiocytoid mesothelioma, an immunohistochemical panel of antibodies for pathological staining is mandatory so that tumors can be differentiated from others that are similar.
In immunohistochemistry, pathologists add antibodies to tumor tissue and look for positive reactions in the tissue proteins. Each cancer has certain positive markers that doctors can look for under a microscope to make a more accurate diagnosis.
For lymphohistiocytoid tumors, the tissue is usually fixed in a block of paraffin, thinly sliced and mounted on a slide. In immunohistochemical studies, cytokeratin, vimentin, calretinin and CH5/6 were proteins strongly expressed by the histiocytoid cells found in the tumor. They are negative for lymphoid and macrophage markers. To differentiate it from other cancers such as lymphoepithelial-like carcinoma reaching the pleura or a pleural-based thymic epithelial tumor, the antibodies AE1/AE3 and calretinin are the most reliable for staining tissue samples.
Symptoms, Treatment and Prognosis
Symptoms of lymphohistiocytoid mesothelioma are similar to other types of pleural mesothelioma and may include chest pain, weight loss and fatigue. Although information on treating this type of mesothelioma is limited, patients have generally been treated with surgery, chemotherapy and radiation therapy.
Surgery
Chemotherapy
Radiation Therapy
Some of the earliest cases of lymphohistiocytoid mesothelioma that were described in 1988 reported no positive response to chemotherapy or radiation. The three patients treated survived for four months, five months and eight months. However, a 2007 study evaluating 22 cases showed much improvement in positive response to treatment and extended life span, with survival ranging between 32 and 40 months after diagnosis.
In an encouraging individual case study, a spontaneous regression of the tumor was reported. Doctors surgically removed tumors from the patient, and 12 years after initial presentation he remained alive and well with no symptoms. In a small number of studies of this rare subtype, there were reports of survival of as much as six years after diagnosis. Some doctors suggest that the immune cells found in this tumor may have a connection to spontaneous regression.
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