A phase III study of nivolumab (NIVO), NIVO + ipilimumab (IPI), or chemotherapy (CT) for microsatellite instability-high (MSI-H)/mismatch repair-deficient (dMMR) metastatic colorectal cancer (mCRC): Checkmate 8HW.

TPS266 Background: Patients (pts) with MSI-H/dMMR mCRC treated with CT have poorer outcomes than pts with microsatellite stable/MMR proficient mCRC. NIVO (anti–programmed death [PD]-1) and IPI (anti–cytotoxic T lymphocyte antigen-4 [CTLA-4]) are immune checkpoint inhibitors that act synergistically and promote antitumor immune response by complementary mechanisms. NIVO±IPI received accelerated US FDA approval for MSI-H/dMMR mCRC that progressed after fluoropyrimidine, oxaliplatin, and irinotecan treatment based on the phase 2, non-randomized, multicohort CheckMate 142 study. Indirect comparisons suggest that NIVO (3 mg/kg) + low-dose IPI (1 mg/kg) provides improved clinical benefit vs NIVO (investigator-assessed [INV] objective response rate [ORR] 55% vs 31%; 12-month [mo] INV progression-free survival [PFS] rate 71% vs 50%; 12-mo overall survival [OS] rate 85% vs 73%) with a favorable benefit-risk profile for previously treated MSI-H/dMMR mCRC (Overman et al. JCO 2018). NIVO+low-dose IPI also demonstrated robust and durable clinical benefit in first-line MSI-H/dMMR mCRC (INV ORR 64%; 12-mo INV PFS rate 77%; 12-mo OS rate 84%; Lenz et al. ASCO 2019, #3521). To date, no prospective phase 3 studies have reported results for anti–PD-1, anti–PD-1 + anti–CTLA-4, or CT in MSI-H/dMMR mCRC; these treatments will be evaluated in the international, multicenter, open-label, randomized, phase 3 CheckMate 8HW (NCT04008030) study. Methods: Approximately 494 pts aged ≥18 years with histologically confirmed recurrent or mCRC, irrespective of prior treatment with CT and/or targeted agents, not amenable to surgery, and with known tumor MSI-H or dMMR status, and Eastern Cooperative Oncology Group performance status ≤1 will be randomized to receive NIVO, NIVO+IPI, or investigator’s choice CT (pts in the CT arm can receive NIVO+IPI upon progression). The primary endpoint is PFS, assessed by blinded independent central review (BICR). Secondary endpoints include PFS by INV, ORR and disease control rate by BICR and INV, OS, time to and duration of response. Exploratory endpoints include safety. Clinical trial information: NCT04008030.