Malignant mesotheliomas are rare cancers that form in the tissues lining the lungs (pleura), abdomen (peritoneum) or heart (pericardium). Pleural mesothelioma, which affects the lining of the lungs, is the most common, accounting for about 75 percent of all malignant mesotheliomas. Between ten and twenty percent of all malignant mesotheliomas are peritoneal mesotheliomas. Pericardial mesotheliomas are extremely rare. A history of exposure to asbestos is found in most individuals with mesothelioma. The time from exposure to onset of cancer may be as long as thirty years; this is why most people with malignant mesothelioma are between 50 and 70 years old.

Many symptoms of malignant mesothelioma are non-specific, and are also seen in a number of other chest and abdominal conditions. This, combined with the lack of an accurate history of asbestos exposure in some patients, may considerably delay diagnosis. The majority of people with mesothelioma only have symptoms during the two to three months before they are diagnosed. About one quarter of all people with malignant mesothelioma have symptoms for about six months before diagnosis.

Once symptoms are present, they may depend on the location of the primary cancer. In general, symptoms become more pronounced with more advanced disease. With pleural mesothelioma, common symptoms are difficulty breathing, cough, pain in the chest or under the ribcage, coughing up blood, hoarseness, and the collection of fluid or pleural effusion in the pleural cavity. The face and arms may swell up. Many of these symptoms and signs are also seen with lung cancer.

With peritoneal mesothelioma, symptoms may include a lump or swelling in the abdomen, abdominal pain, fluid in the abdomen, constipation due to bowel obstruction, nausea, vomiting, and loss of appetite. Patients suffering from pericardial mesothelioma may experience chest pain, breathlessness and palpitations. Some symptoms of malignant mesothelioma are common to many cancers. These include unexplained weight loss, fever and fatigue.