Histidine and Immunotherapy Response in Colorectal Cancer

Inclusion Criteria: 1. Participants aged ≥18 years and ≤100 years. 2. Patients pathologically diagnosed with colorectal cancer based on colonoscopy or surgical specimens and biopsy examination; or patients who previously received PD-1 monoclonal antibody immunotherapy for colorectal cancer. Exclusion Criteria: 1. Age \<18 years. 2. Presence of poorly controlled metabolic diseases, including hypertension, diabetes mellitus, hyperlipidemia, hyperuricemia, or hyperthyroidism. 3. Presence of other severe gastrointestinal diseases, including inflammatory bowel disease, ischemic bowel disease, familial adenomatous polyposis, liver cirrhosis, MUTYH-associated polyposis (MAP), Lynch syndrome (LS), or Peutz-Jeghers syndrome (PJS). 4. History of other malignant tumors, or pathological diagnosis of colorectal inflammatory polyps, hyperplastic polyps, neuroendocrine tumors, neuroendocrine carcinoma, or mixed neuroendocrine-non-neuroendocrine neoplasms. 5. History of neurological or psychiatric disorders, such as epilepsy or depression. 6. Unqualified specimens, including hemolyzed serum samples or tissue samples that were not properly preserved in time.