Mesothelioma is an aggressive cancer affecting the membrane lining of the lungs and abdomen. Malignant mesothelioma is the most serious of all asbestos-related diseases. Although uncommon, mesothelioma cancer is no longer considered rare. The primary cause and risk factor for mesothelioma is exposure to asbestos. Making a correct mesothelioma diagnosis is particularly difficult for doctors because the disease often presents with symptoms that mimic other common ailments. There is no known cure for mesothelioma, but treatments such as surgery and chemotherapy have helped to improve the typical mesothelioma prognosis. There are many different kinds of cells that can make up a mesothelioma tumor, which can make it very difficult to formulate a definitive diagnosis. After a biopsy is taken, pathologists are often unable to say with certainty whether cells taken from the lungs or abdomen are for sure mesothelioma, as they can often look very similar - if not nearly identical - to other types of cancers found in the same parts of the body. Because of this, patients will often have to undergo a large number of tests to rule out other possible problems, and may even need a surgical biopsy to address the problem internally.