Targeting EZH2 to overcome the resistance to immunotherapy in microsatellite stable colorectal cancer: Results from the CAIRE study

3599 Background: Profound epigenetic and transcriptomic changes induced by EZH2 in tumor cells and immune cells mobilize the elements of the TME, leading to immune-suppressive activity of solid tumors. Targeting EZH2 can enhance anti-tumor immunity by reshaping the tumor microenvironment (TME). The CAIRE study is first study investigating the impact of EZH2 inhibition in combination with immune checkpoint inhibitor in solid tumors. Methods: This is a single-arm open-label multicentric phase II trial assessing the efficacy and safety of tazemetostat (800 mg BID) combined with durvalumab (1120 mg every 3 weeks) in patients with advanced microsatellite stable colorectal cancer. The primary endpoint was the disease control rate within 24 weeks after treatment onset defined as the proportion of patients with at least a tumor assessment showing connfirmed or unconfirmed complete response, confirmed or unconfirmed partial response or stable disease based on central review according to RECIST 1.1. Secondary endpoints included: 1-year progression free survival (PFS), 1-year overall survival (OS), and safety using NCI-CTCAE v5.0. All patients underwent sequential blood and tissue sampling for translational studies. Results: Between July 2021, and June 2022, 47 pts were enrolled at Institut Bergonié (Bordeaux, Centre). Median age was 67.7 (range 39.6 – 84.0). Median number of previous treatment lines was 4: (range 1 – 6). The most common treatment related adverse events were grade 1/2 asthenia, nausea. No death was related to the treatment. Among the 34 pts for whom blinded central review of imaging was available for at least one imaging tumor assessment, best tumor response was confirmed partial response, stable disease and progressive disease in 1 (2.9%), 11 (32.3%) and 22 (64.7%) patients respectively. The disease control rate was 35.3% (95%CI 19.7 – 53.5). Conclusions: The CAIRE study met its first endpoint for disease control rate in patients with advanced colorectal cancer. Efficacy data on the whole cohort of patients and full biomarkers analyses will be presented at the meeting. Clinical trial information: NCT04705818 .