Background: ATP release from dying cancer cells in response to platinum-based chemotherapy increases extracellular immunosuppressive adenosine, which binds and activates the A_2a and A_2b receptors on immune cells. Adenosine-mediated signaling impairs activation, proliferation, and cytotoxic activity of effector T cells, resulting in inhibition of antitumor activity. Concomitant adenosine receptor blockade may therefore enhance the therapeutic efficacy of chemo/immunotherapy regimens. Etrumadenant (AB928), the first clinical-stage, small-molecule, dual adenosine receptor antagonist, is highly potent, pharmacodynamically active, and has been well tolerated in dose escalation studies as monotherapy or combined with chemo/immunotherapy. Recently, results were reported for the ARC-3 phase 1/1b study of etrumadenant + modified 5-fluorouracil + oxaliplatin (mFOLFOX-6) in patients (pts) with mCRC. In this study, etrumadenant + mFOLFOX-6 was well tolerated without significant additive toxicity. Disease control was observed in patients with RAS/BRAF mutated mCRC, as well as 3L+ disease previously treated with FOLFOX and/or FOLFIRI (PR and/or SD >4 mo). Due to deep responses in 1L-3L+ pts, 6 pts had the opportunity to pursue surgery and radiotherapy with curative intent. The encouraging results from ARC-3 warrant further evaluation of etrumadenant-based combination therapy for mCRC. Methods: ARC-9 is a phase 1b/2, multicohort, open-label, randomized platform study designed to evaluate safety and clinical activity of etrumadenant (150 mg orally once daily [QD]) in combination with standard-of-care (SOC) regimens or novel therapeutics in pts with mCRC (Table). Cohort eligibility is based on prior anticancer treatment history. Pts enrolled in Cohorts A and B will be randomized (2:1) into the experimental vs SOC arms. Cohort C consists of a single arm to allow inclusion of novel agents as they become available with built in early stopping rules for futility. Pts who progress on the SOC arm of Cohort A can enroll in Cohort B; pts who progress on the SOC arm of Cohort B can crossover to the experimental arm. Primary endpoints across cohorts are shown in Table. Safety monitoring will occur throughout the trial, disease assessments will occur every 8 weeks, and correlative study pre- and on-treatment biopsies will be performed.

^a Administered if Bev is not contraindicated. Bev, bevacizumab; Etruma, etrumadenant; IRI, irinotecan; L, line; ORR, objective response rate; OS, overall survival; PFS, progression-free survival