A patient with peritoneal mesothelioma may not demonstrate symptoms for 20 to 50 years following asbestos exposure. Once asbestos fibers have irritated and caused mesothelial cells to become inflamed, the peritoneum starts to thicken. The buildup of fluid, known as ascites, is the next phase of cancer progression for some patients. Overtime, mesothelioma tumors form and this places pressure on internal organs.