Regorafenib in Combination With Pembrolizumab or Pembrolizumab for MSI-H Colorectal Cancer

Regorafenib is a multi-kinase inhibitor that targets several receptor tyrosine kinases including vascular endothelial growth factor receptor (VEGFR). Regorafenib may also have immunomodulatory affect in the tumor microenvironment. Preclinical and early clinical studies indicate there is a potential for synergistic activity of regorafenib with immune checkpoint inhibitors that can be leveraged to augment antitumor immunity. Pembrolizumab, anti-PD1 blockade, has been approved for patients with high microsatellite instability (MSI-H) colorectal cancer (CRC) as first line therapy. However, there is still an unmet need to enhance the efficacy of immune checkpoint inhibitors for patients with MSI-H colorectal cancer. The efficacy of TKI and immune checkpoint inhibitor combination have been shown in clinical studies for solid tumors particularly for those that are responsive to immune checkpoint inhibitors therapy. Therefore, there is strong rationale for the combination of regorafenib and pembrolizumab in MSI-H colorectal cancer in which there is increased VEGF activity compared to MSS counterpart. A recent retrospective study showed significantly improved response to regorafenib among patients with MSI-H colorectal cancer, compared to patients with MSS colorectal cancer. Collectively, this combination may increase anti-tumor immune response and clinical effectiveness of immunotherapy for patients with MSI-H colorectal cancer. Based on prior clinical trials, the target regorafenib dose in this study is determined to be 90 mg. However, patients in the lead-in phase will receive regorafenib 60 mg in combination with 200mg of pembrolizumab Q3 weeks in the first cycle to increase tolerance and study compliance. The dose of regorafenib will be increased to 90 mg by Cycle 2. An interim analysis will be performed after completion of data collection for the lead-in phase. Target enrollment for the lead-in phase is approximately 22 patients. Following the futility analysis in lead-in phase, the randomized phase target enrollment is determined to be 66 patients per arm, for a total trial enrollment of 154 participants. Patients who received 3 or less cycles of chemotherapy prior to the determination of MMR-D and MSI-H disease can be enrolled in this trial.