Combining low-dose regorafenib with pembrolizumab for patients with MSI-H colorectal cancer: REGPEM-CRC-01.
Authors: Sahin Ibrahim Halil , Chakrabarti Sakti , Hsieh Ronan Wenhan , Bruno Tullia C. , Selfridge Jennifer Eva , Gorantla Vikram , Thomas Roby Antony , Rhee John C. , Tatsuoka Curtis , Bajor David L. , Mahipal Amit , Chiorean E. Gabriela , Tejani Mohamedtaki Abdulaziz , Saeed Anwaar 
Published: January 2024

TPS238 Background: Treatment for microsatellite instability-high (MSI-H)/mismatch repair deficient (MMR-D) colorectal cancer (CRC) has rapidly evolved in the last decade. The KEYNOTE 177 trial recently established pembrolizumab as a frontline therapy for patients with MSI-H CRC. However, in this study, approximately 40% of patients were noted to have disease progression within 6 months of treatment. Furthermore, an additional 10% of patients experienced acquired resistance to therapy. Therefore, there is an unmet need to improve outcomes for patients with MSI-H CRC. Preclinical studies have shown vascular endothelial growth factor (VEGF) signaling to be overactive in MSI-H compared to MSS CRC (Hansen et al. Colorectal Dis. 2011). Moreover, exploratory analysis of CALBG-80405 and PARADIGM trials showed that patients with MSI-H CRC were more likely to benefit from anti-VEGF therapy than those with MSS disease. Regorafenib, an FDA-approved agent for patients with mCRC, is a potent VEGF inhibitor with immune modulatory effects on the tumor microenvironment. We hypothesize that adding low-dose regorafenib to pembrolizumab as frontline therapy may create synergistic activity in addition to the known clinical activity of each agent in MSI-H CRC. Methods: In the lead-in arm of this prospective study, 22 patients will be enrolled. Patients will receive regorafenib 60 mg daily on days 1–14 (2 weeks on) followed by 7 days off (1 week off) in combination with pembrolizumab 200 mg in the cycle 1. In the following cycles, patients will receive regorafenib 90 mg daily for 2 weeks on 1 week off in combination with pembrolizumab 200 mg every 3 weeks. The primary outcome for the lead-in arm is overall response rate (ORR) within 12 months of treatment by RECIST 1.1. criteria. A formal one-sided hypothesis test will be conducted for futility, assuming that we will reject the null hypothesis of a target ORR only if we have strong evidence. In this study, we assume a null hypothesis that ORR is 0.60, which would reflect significant clinical improvement over the current standard of ORR = 0.43 from KEYNOTE 177. The alternative hypothesis is that ORR is less than 0.60. For the lead-in phase of the study, the emphasis is on controlling Type I error to be small, approximately 0.05. In the randomized phase of the study, patients will receive pembrolizumab monotherapy or pembrolizumab in combination with regorafenib 90 mg. The sample size for the randomized phase of trial was determined based on an assumed median of PFS of 28 months with pembrolizumab and regorafenib combination (investigational arm). The standard of care pembrolizumab monotherapy results in a median PFS of 16 months when given as a first-line therapy. We hypothesize the proposed treatment will increase median PFS to 28 months from 16 months (N=132; H0: 16 months vs., H1: 28 months; Type I error: 0.05, power 80%). Clinical trial information: NCT06006923 .