TPS156 Background: The trifunctional anti-EpCAM/anti-CD3 antibody catumaxomab was recently approved in the EU for intraperitoneal (i.p.) treatment of malignant ascites, based on data from an international, randomized clinical trial (Parsons et al. J Clin Oncol 2008; 26:abst 3000). In the PK analysis, the i.p. application of 10-20-50-150μ g catumaxomab resulted in high and effective local i.p. concentrations. As reported (Ruf et al. J Clin Oncol 2008; 26: abst 14006) the systemic catumaxomab exposure was low (< 5%) with a maximum median plasma concentration (C max) of 403 pg/ml and a mean plasma elimination half-life of 2.13 days. Nevertheless, catumaxomab remained immunologically active even after several days in the circulation. In the pivotal trial patients showed clinical benefit regardless of absence or presence of distant metastases (Heiss et al WCGIC 2009). Futhermore, an overall survival benefit in the gastric cancer subgroup was reported (Heiss et al ECCO/ESMO 2009). First anecdotal reports from patients treated with i.p. catumaxomab indicate a potential antitumor effect on extraperitoneal tumor sites. So far, there are no clinical study data available on a systemic treatment effect on the primary tumor site or distant metastases following locoregional i.p. catumaxomab administration. Therefore, relevant data will be collected systematically within this prospective observational trial. Methods: A planned number of 150 patients with malignant ascites due to epithelial cancer (ovarian, breast, and GI cancer) treated with catumaxomab i.p. under routine conditions in clinical practice will be closely documented. Data concerning underlying cancer disease, demographic factors, immunological parameters, applied chemotherapeutic regimen, tumor staging, safety results and clinical outcome will be collected and analyzed by descriptive statistical methods for the overall population and stratified by each cancer subpopulation. Targeted tumor lesions will be followed before and after catumaxomab via RECIST criteria. Interim analysis will be performed after each 50 patients. Author Disclosure Employment or Leadership Position Consultant or Advisory Role Stock Ownership Honoraria Research Funding Expert Testimony Other Remuneration Fresenius Biotech, Fresenius Biotech GmbH, TRION Pharma GmbH, TRION Research GmbH TRION Pharma GmbH