Stomach or abdominal symptoms are often experienced by patients with peritoneal mesothelioma. This type of mesothelioma is a cancer of the peritoneal cells that line the abdomen. Symptoms of peritoneal mesothelioma are insidious and often tend to be confused for symptoms of more common, and often more benign, abdominal conditions. Peritoneal mesothelioma therefore may go undiagnosed until it is fairly advanced and resistant to treatment.

Common abdominal symptoms of peritoneal mesothelioma include nausea, vomiting, and loss of appetite. An abdominal lump or swelling may be present. Such a lump or swelling may obstruct the bowel, causing constipation. Fluid may collect in the abdominal cavity, causing distension and bloating. This collection of fluid in the abdominal cavity is called ascites, and is also seen in people with liver disease. The fluid is often drained to relieve symptoms of bloating and distension; excessive fluid collection may hamper normal breathing. The collection of fluid in the abdomen, and the pressure of a cancerous growth, may impede the return of blood flow from the legs, leading to swollen feet. Such swelling of the extremities is also seen in kidney disease and pregnancy.

Some recent studies have shown a transient reduction in tumor mass and fluid collection following the introduction of certain substances into the abdominal cavity; however, these effects have been shown on a small number of patients and are being researched further.

Abdominal pain in peritoneal mesothelioma may be caused by the pressure on organs and nerves exerted by a growing tumor, by distension of the bowel, or by infiltration of adjacent tissues and organs by cancerous cells. Narcotic pain-relieving drugs or radiotherapy may be used to relieve severe pain. Abdominal symptoms and the systemic effects of cancer can cause severe weight loss in people with peritoneal mesothelioma. Fever and fatigue are also common.