The aim of this study is to determine whether dMMR/MSI-H and/or POLE exonuclease domain mutant stage III colon cancer patients gain clinical benefit (ie, improvement in disease-free and OS) from PD-L1 inhibition after standard fluoropyrimidine-based adjuvant chemotherapy and to examine whether this is a cost-effective approach for the National Health Service. Here, POLE is linked to malignant colon neoplasm.