Background: Most colon cancer (CC) patients can be treated with upfront curative surgery; however, relapse often occurs and the disease becomes deadly. Neoadjuvant chemotherapy does not jeopardize timing or quality of surgery and enhances relapse-free outcomes in proficient mismatch-repair (pMMR) CC (Morton et al, J Clin Oncol 2023). In the same setting, the use of immune checkpoint inhibitors (ICIs) with a single dose of ipilimumab (Ipi) and two doses of nivolumab (Nivo) proved to be feasible without delaying surgery and resulting in 23% major pathological responses (mPR) (Chalabi et al, ASCO 2022). We have previously shown that high dose vitamin C (HDVitC) triggers tumor infiltration and activation of CD8+ T cells in mouse tumors, enhancing efficacy of ICIs in pMMR CC preclinical models (Magrì et al, Sci Transl Med 2020). Methods: ALFEO is an open-label pilot trial of neoadjuvant CC treatment to test whether HDVitC can enhance the efficacy of ICIs in this setting. Main inclusion criteria are pMMR CC stage cT4N0/TxN1-2/[cM1 liver-limited disease with favorable oncological criteria candidate for upfront surgery on both T and M after multidisciplinary team evaluation]. Patients will receive Nivo i.v. 3 mg/kg D1 and D15, Ipi i.v. 1 mg/kg D 1 and VitC 70 g/ m² D1-3 and 15-17. Tumor assessment will be performed at D21-28, followed by surgery within D28. Primary objective is activity of Nivo/Ipi + HDVitC; secondary objective is safety; exploratory objectives are correlation between efficacy and pharmacodynamic including tumor microenvironment changes. Primary endpoint is mPR rate. Considering the proof-of-principle nature of the trial, a design with a boundary for early stopping (both futility/utility and toxicity) and a fixed maximum sample size of 24 patients has been chosen. mPR for the Ipi/Nivo has been set at 23% (H₀), while H₁ at 75%. A Bayesian hypothesis test-based design (Zhou et al, Pharm Stat 2021) will be used for decision-making. Su. Clinical trial information: ECTR2022-502101-15-00.