Results of a phase II randomized study evaluating the potential benefit of a postoperative intraperitoneal immunotherapy after resection of peritoneal metastases from gastric carcinoma metastases (IIPOP- NCT01784900).

4064 Background: Prognosis of patients with peritoneal extension from gastric carcinoma remains poor. The aim of this multicentre, open-label, phase 2 randomized study was to analyze the potential survival benefit of an immediate postoperative intraperitoneal immunotherapy using a bi-specific (anti-EpCAM, anti-CD3), trifonctional agent named catumaxomab. Methods: Patients with limited synchronous carcinomatosis from gastric carcinoma (Peritoneal cancer index (PCI) ≤ 12), were treated after complete resection (gastrectomy plus all peritoneal deposits), by an intraperitoneal infusion of catumaxomab during 5 days. Patients were randomized between 2 arms according to the total doses administered of catumaxomab (100µg vs 140µg). The first end-point was the 2-year overall survival (OS). Forty randomized patients were required (20 in each arm), considering that a 2-year OS rate ≤ 30% would be considered as unacceptable, and ≥ 55%, a promising survival rate. The study was stopped prematurely due to the manufacturing stop of the catumaxomab. Results: Between March 2013 and September 2014, 26 patients were included in the study; among them, 11 were randomized, with a median PCI of 9 [1-12]. Seven patients received the whole planned treatment of catumaxomab; in the remaining 4 patients, interruptions were related to postoperative complications. One patient died postoperatively of multiorgan failure and grade 3-5 complications occurred in all the patients, without difference between the 2 groups. At the end of the follow-up, 3 were alive (25, 30, 36 months). The median OS was 19 months, and the 1 and 2- year OS rates were 63.6% and 36.4% respectively. Conclusions: This study has to be stopped prematurely; however, encouraging results regarding overall survival were observed. Intraperitoneal immunotherapy represents an innovative and promising treatment in patients with peritoneal metastases, considering the poor response to systemic chemotherapy and the “immunocompetence” of the peritoneum. The evaluation of a potential benefit of a local immunotherapy has to be pursued. Clinical trial information: NCT01784900.