METEORITE: A phase II study of Y-90, capecitabine, and atezolizumab in oligometastatic CRC (BrUOG430).

TPS276 Background: Colorectal cancer (CRC) is the second leading cause of cancer death in the United States. Patients with microsatellite-stable (MSS), chemotherapy-refractory metastatic CRC have limited treatment options, with third-line treatment offering modest survival benefits. Yttrium-90 (Y-90) radioembolization is an established locoregional therapy that provides intrahepatic disease control, while also exerting immunomodulatory effects that may enhance responsiveness to checkpoint inhibition. Atezolizumab, an anti–PD-L1 antibody, has demonstrated tolerability in CRC in combination with chemotherapy but limited single-agent activity in MSS disease. Capecitabine is a known radiosensitizer commonly used in conjunction with radiation therapy. We hypothesize that Y-90, in combination with capecitabine and atezolizumab, will synergistically improve intrahepatic disease control in patients with chemotherapy-refractory, unresectable, liver-isolated or liver-dominant metastatic CRC. Methods: METEORITE (BrUOG-430) is a prospective, single-arm, phase II pilot trial evaluating Y-90 microspheres with concurrent capecitabine and atezolizumab. Eligible patients must have histologically confirmed CRC with surgically unresectable, liver-isolated or liver-dominant, RECIST-measurable liver metastases, with