Does the development of malignant ascites mean much shortened survival in cancer patients?

Generally yes: If the ascites is caused by studding of the peritoneum with tumor or thrombosis of the portal vein, then the cancer is much advanced. Some centers may offer hyperthermia for peritoneal carcinomatosis and i've heard success stories; a thrombosed portal vein might sometime be successfully treated. Today's physicians are honest about your odds and the risk-cost / benefit ration you can expect.

Qualified yes.: Malignant ascites (fluid in the abdominal cavity that shows tumor cells) mean that cancer has spread in the visceral organs in the abdomen. This situation puts the patient in higher stage of cancer and can signficantly determine the mode or kind of treatment. In general, patients have a shorter survival, however, I have known patients who lived longer after aggressive chemotherapy.