Peritoneal Mesothelioma Not Caused by Asbestos Malignant peritoneal mesothelioma forms in the lining of the abdomen. It is less prevalent than the pleural type and more women are affected than men. The symptoms of peritoneal mesothelioma may be vague, such as abdominal discomfort, weight loss, constipation or diarrhoea. A mesothelioma