A condition in which cancer causes extra fluid to collect between the thin layers of the peritoneum (tissue that lines the abdomen and covers most of the organs in the abdomen). Signs and symptoms may include pain or swelling in the abdomen, trouble breathing, chest pain, weight gain, nausea, loss of appetite, and fatigue. Malignant peritoneal effusions are most often caused by cancers of the ovary, uterus, breast, colon, lung, pancreas, and liver.