Malignant ascites represents a severe clinical problem for physicians and patients being confronted with this common symptom of advanced-stage gastrointestinal cancer. Unfortunately, there is no standardized and evidence-based treatment for malignant ascites and therapies which are commonly being used are only temporarily effective. Newer modes of therapy, such as the application of the tri-functional antibody catumaxomab, are associated with significant side effects and are limited to patients in stages of good overall performance. Therefore, there is still an urgent need for more effective, longer-lasting, and less toxic modes of treatment for peritoneal effusions caused by gastrointestinal cancers.