This observational study aims to investigate the role of histidine and its transporter SLC15A3 in modulating the sensitivity of colorectal cancer to immunotherapy. By analyzing the expression of SLC15A3 in tumor/normal colonic tissues from patients with colorectal cancer and assessing serum histidine metabolic levels, the study seeks to identify potential targets associated with therapeutic resistance and explore possible intervention strategies to improve immune checkpoint blockade treatment efficacy.