Association of humoral antitumor response with clinical benefit in catumaxomab-treated malignant ascites patients: Results from a phase IIIb study.

2584 Background: The bispecific antibody catumaxomab (anti-EpCAM x anti-CD3) which is approved for the treatment of malignant ascites (MA) patients (pts) in the EU elicits a humoral immune response against tumor-associated antigens. Here we present follow up data analyzing the influence of this antibody response on puncture free (PFS) and overall survival (OS). Methods: In the course of the phase IIIb study CASIMAS, MA pts with EpCAM positive tumors were treated with/without prednisolone premedication by 4 infusions of 10, 20, 50 and 150 µg of catumaxomab over 11 days (d). EpCAM and HER2-specific antibody responses in plasma samples of 23 pts were measured by ELISA. Additionally, samples of 5 pts receiving a second treatment cycle were analyzed. Pts with significant increase (≥ 2) or de novo development of anti-tumor antibodies within 38 d after treatment start were defined as responders (R). Non responders (NR) showed no humoral response by d 38 or died before. PFS and OS of R and NR were compared by Kap...