Background: Recent studies have shown shown that genetic depletion of EZH2 in Tregs (using FoxP3creEZH2fl/fl mice) and pharmacological inhibition of EZH2 elicits phenotypic and functional alterations of Tregs, leading to an effector-like T cell profile. Further, EZH2 inhibition enhances the cytotoxicity of human Teffs in vitro and the proportion of tumor-infiltrating cytotoxic T cells in vivo in murine models. It has been shown that immune checkpoint inhibition (ICI) increases EZH2 expression in human T cells across various tumor types and that increased EZH2 expression in T cells inversely correlate with clinical outcome. Upregulation of EZH2 mediated by immune checkpoint inhibition in T cells modulates T cell responses and diminishes the effectiveness of immunotherapy. Consistent with this mechanism, pharmacologic inhibition of EZH2 has been shown to increase effector-like T cell responses and enhances effectiveness of immune checkpoint therapy in tumor-bearing mice [16-17]. Our group also reported first clinical data from a participant with sarcoma showing strong T cell infiltration after treatment with tazemetostat (Italiano et al Lancet Oncol 2018). Altogether, these findings pave the way for clinical trials combining ICI with the specific EZH2 inhibitor, tazemetostat in solid tumors. Methods: CAIRE (NCT04705818) is a multi-cohort, four single-arm phase 2, multicenter, open-label study investigating tazemetostat combined with durvalumab in patients with advanced cancers: pancreatic adenocarcinoma (cohort A), microsatellite stable colorectal cancer (cohort B), solid tumors with presence of tertiary lymphoid structures (assessed centrally) (cohort C), soft-tissue sarcomas (cohort D). Cohort A will enroll ̃32 patients and cohorts B, C and D ̃47 patients respectively. Eligible patients must have no standard treatment options available or a contraindication to standard treatment options, and ECOG PS 0–1. Patients with prior exposure to EZH2 inhibitor and/or PD1/PDL1 monoclonal antibodies are excluded. Tazemetostat will be administered per-os, twice daily (800 mg x 2), continuously. Treatment by Tazemetostat will start on Day 1 (of cycle 1). Durvalumab will be administered by intravenous infusion (1120 mg) on day 1, every 3 weeks. Treatment by Durvalumab will start on Day 1 of cycle 2. The primary endpoints are disease control rate within 24 weeks of treatment as per RECIST 1.1 in cohort A and B; objective response rate within 24 weeks of treatment as per RECIST 1.1 in cohort C, and 6-months non progression rate for cohort D. Secondary endpoints include adverse events (AEs)/serious AEs, duration of response, and progression-free survival. Pharmacodynamic and other biomarkers will be explored. The first patient received study drug on July, 30, 2022 and 1 site across France are currently enrolling patients. Clinical trial information: NCT04705818.