490 Background: In 2009 the trifunctional antibody catumaxomab was approved for the intraperitoneal (i.p.) treatment of malignant ascites (MA) in EpCAM-positive carcinomas in Europe. Overall survival (OS) results for gastric cancer patients from the pivotal trial showed a significant treatment benefit of catumaxomab in this patient group. We present the results for the gastrointestinal (GI) cancer subgroup from the pivotal trial including long-term survivors. Methods: A total of 86 patients with MA due to GI cancer (gastric, pancreatic, colon, esophagus, rectum carcinoma) were treated with paracentesis plus catumaxomab (59 patients) vs. paracentesis alone (control, 27 patients). The primary endpoint was puncture-free survival; main secondary endpoints were time to next puncture, overall survival and safety parameters. The endpoints were compared between the catumaxomab and the control group using the Kaplan-Meier method and log-rank test. Analyses were performed for the Full Analysis Set (FAS) and the Safety Set (patients who received at least 1 catumaxomab infusion; 95%). Results: For puncture-free survival, a median of 35 days for catumaxomab vs. 14 days for control was observed (p<0.0001, HR: 0.340 with 95 % CI from 0.194 to 0.597, FAS). Time to next puncture resulted in a median of 118 days vs. 15 days (p<0.0001, HR: 0.161 with 95 % CI from 0.069 to 0.378, FAS). Although the study was not powered nor designed for OS, the difference between treatment and control arm was significant for the Safety Set (median: 61 vs. 44 days, p<0.05, HR: 0.553). ADRs were generally mild to moderate, limited to the treatment period and reversible. Conclusions: I.p. catumaxomab is an EMA-approved treatment for patients suffering from malignant ascites. The positive efficacy results were demonstrated in an advanced stage patient population together with a predictable and manageable safety profile. Patients suffering from peritoneal carcinomatosis with malignant ascites due to GI cancers experience a significant survival benefit from i.p. treatment with catumaxomab. [Table: see text]