TPS268 Background: 5-fluorouracil (5FU), in combination with folates, is an established cornerstone of metastatic colorectal cancer (mCRC) treatment. All folates currently approved for mCRC need to be metabolically activated to [6R]-5,10-methylenetetrahydrofolic acid ([6R]-MTHF), the active thymidylate synthase co-substrate that potentiates the effect of 5FU. Arfolitixorin does not require multi-step metabolic activation, and may produce higher, and less inter- and intraindividually variable, concentrations of [6R]-MTHF than leucovorin. Methods: The phase III AGENT trial (NCT03750786) is a randomized, multicenter, parallel-group study comparing the efficacy of arfolitixorin versus leucovorin in mCRC patients treated with first-line 5FU, oxaliplatin, and bevacizumab. Patients are randomized (1:1) to the investigational arm (arfolitixorin + 5FU + oxaliplatin [ARFOX] + bevacizumab) or the comparator arm (leucovorin + 5FU + oxaliplatin [modified FOLFOX-6] + bevacizumab), and treated until disease progression based on RECIST 1.1 criteria. Recruitment is ongoing, and aims to randomize 440 patients in 18 months. Eligibility criteria include non-resectable mCRC; eligibility for 5FU, oxaliplatin, and bevacizumab therapy; ECOG PS 0 or 1. The study will be conducted across approximately 100 sites in Australia, Austria, Canada, France, Germany, Greece, Japan, Spain, Sweden, and USA. The primary endpoint is objective response rate. Key secondary endpoints are progression-free survival and duration of response. Additional secondary endpoints include overall survival, quality of life, safety and tolerability, and number of patients undergoing curative metastasis resection. A translational program will evaluate expression levels of several folate metabolism- and transportation-related genes in mCRC tumor biopsies to determine their relationship to treatment outcome. A broad array of genes will analyzed, including ATP-binding cassette C3 (ABCC3) transporter, methylenetetrahydrofolate dehydrogenase 2 (MTHFD2), proton-coupled folate transporter (PCFT), and serine hydroxymethyltransferase 1 (SHMT1). Interim data are expected in mid 2020. Clinical trial information: NCT03750786.