RecruitingPhase 4Drug trialDPYD Pharmacogenomics and Fluoropyrimidine (FP) Dose-AdjustmentTo prospectively evaluate the efficacy and safety of DPYD-guided dosing strategies in a real-world clinical setting, specifically by comparing the incidence of severe (Grade 3 and 4) fluoropyrimidine-related toxicities of heterozygous DPYD variant patients assigned to DPYD-guided reduced dosing versus patients with standard dosing in the control arm.