IMPALA, a randomized phase III study in patients with metastatic colorectal carcinoma: Immunomodulatory maintenance therapy with TLR-9 agonist MGN1703.

TPS791 Background: The potent TLR-9 agonist MGN1703, a synthetic DNA-based immunomodulator, was compared to placebo in metastatic colorectal cancer (mCRC) patients with disease control after standard induction chemotherapy +/- bevacizumab in the phase II IMPACT trial and showed a superior effect with a hazard ratio for the primary endpoint PFS on maintenance of 0.55 (p=0.041) by local investigator assessment and 0.56 (p=0.070) by independent radiological review. In the MGN1703 arm 3 objective responses were observed, two of them appearing as late as 9 months after the start of treatment. At time of study closure 4 MGN1703 patients were still without progressive disease and continued treatment by self-administration in a compassionate use setting. Exploratory Cox regression and ROC analyses suggested a potential predictive role at baseline for normal CEA, objective response to prior chemotherapy and presence of activated NKT-cells. Methods: The pivotal IMPALA study has been designed to confirm these data and started to enroll patients with smaller tumor burden after a good response to chemotherapy, as best candidates to receive a maintenance treatment with immunotherapy. IMPALA is a randomized, international, multicenter, open-label phase III trial that will include 540 patients from 120 centers with the collaboration of the AIO, TTD, and GERCOR cooperative groups and is currently recruiting patients. In this study mCRC patients with an objective tumor response following any first line induction therapy will be randomized to MGN1703 monotherapy maintenance or local standard of care. At time of relapse, patients will reintroduce the induction treatment whenever feasible, with those in the experimental arm continuing to receive MGN1703 in the weeks without chemotherapy. Patients will also be stratified by CEA level and activated NKT at baseline. The primary endpoint of the study will be overall survival. Secondary endpoints include PFS, response rates, safety, and QoL in selected centers. All patients will be evaluated for cytokines and chemokines in serum and the activation status of various immune cell populations. Clinical trial information: NCT02077868.