Malignant mesothelioma (cancer of the mesothelium) is a disease in which cells of the mesothelium become abnormal and divide without control or order. It is a rare form of cancer that most frequently arises from the cells lining the sacs of the chest (the pleura) or the abdomen (the peritoneum). Malignant mesothelioma is closely linked to exposure to asbestos – a natural fiber that was once used in manufacturing a wide variety of industrial and household products. Workers involved in asbestos mining, milling and manufacturing are at the greatest risk for developing malignant mesothelioma. Also at high risk are shipyard workers, workers in the heating and construction industries, and other tradespeople. Family members and others living with asbestos workers have an increased risk of developing malignant mesothelioma, and possibly other asbestos related diseases as well. Cases of malignant mesothelioma have even included people whose only exposure was breathing the air through ventilation systems.

Although reported incidence rates have increased in the past 20 years, malignant mesothelioma is still a relatively rare cancer. Between 1973 and 1984, there has been a threefold increase in the diagnosis of pleural mesothelioma in Caucasian males. From 1980 to the late 1990s, the death rate from malignant mesothelioma in the USA increased from 2,000 per year to 3,000, with men four times more likely to acquire it than women. The actual rates may be even higher however, since it is possible that many cases of malignant mesothelioma are misdiagnosed as adenocarcinoma of the lung, which is difficult to differentiate from mesothelioma.

The average age of diagnosis of malignant mesothelioma is 60. The average survival time varies from 4 to 18 months, and death is usually due to infection or respiratory failure from the progression of the mesothelioma.

A physician may suspect malignant mesothelioma in a patient who has symptoms suggesting this cancer and who reports a history of asbestos exposure. Careful medical examination may also reveal the presence of fluid in the pleural or abdominal cavity. Once malignant mesothelioma is suspected, a number of methods are available to help confirm the diagnosis.

Imaging methods, such as x-rays, CT scans, MRIs and PET scans, help determine the location, size and extent of the cancer, and specifically detect pleural or peritoneal thickening, fluid in the pleural or abdominal cavity, or nodules of cancer cells. However, a definitive diagnosis of malignant mesothelioma can only be made after the examination of cells from abnormal tissue.

A biopsy of abnormal tissue is performed to find out whether the cells in this tissue are cancerous or not. Such tissue can be removed through minimally invasive surgery. Fluid in the pleural or abdominal cavity may also contain cancer cells, and may also be removed for analysis. Cells from abnormal tissue or fluid are examined under the microscope, and can be identified as normal or cancerous. However, such examination does not necessarily confirm the type of cancer. Cells found in pleural mesotheliomas can resemble lung cancer cells, and cells found in peritoneal mesotheliomas can resemble ovarian cancer cells. To differentiate between these different forms of cancer, a method called immunohistochemistry is often used. This method detects proteins on the surface of cancer cells that are specific to certain types of cancers. A newer method called DNA microarray analysis examines the genes of cancer cells. Malignant mesothelioma cancer cells have different gene patterns from other cancer cells and from normal cells.

While no blood tests confirm a diagnosis of malignant mesothelioma, there are certain blood abnormalities that suggest the presence of a cancer. Recent research suggests that elevated levels of a blood protein called osteopontin may help in the early detection of mesothelioma.