Tehran University of Medical Sciences Iranian Journal of Allergy, Asthma and Immunology 1735-1502 0 0 2026 05 30 1 15 Jixiang Liu Department of Health Insurance Affairs, The First Affiliated Hospital of Qiqihar Medical University, Qiqihar, China Shan Liu Department of Clinical Laboratory, The Second Affiliated Hospital of Qiqihar Medical University, Qiqihar, China Jinghang Cong Department of Clinical Laboratory, The Second Affiliated Hospital of Qiqihar Medical University, Qiqihar, China Xuesong Zhao Department of Clinical Laboratory, The Second Affiliated Hospital of Qiqihar Medical University, Qiqihar, China Liwei Zhang Department of Gastroenterology, The Second Affiliated Hospital of Qiqihar Medical University, Qiqihar, China Wei Li Department of Clinical Laboratory, The Second Affiliated Hospital of Qiqihar Medical University, Qiqihar, China 2025 10 28 2026 01 27 Colon cancer, a leading cause of death, demands early detection. We evaluate serum S100 calcium-binding protein A12 (S100A12) and diamine oxidase (DAO) effects on gut dysbiosis/immunity and their combined diagnostic value. This retrospective study included 105 colon cancer patients (study group), 90 benign lesions, and 105 matched healthy controls. Serum S100A12 and DAO were measured by ELISA (enzyme-linked immunosorbent assay). Gut flora (Escherichia coli, Enterococcus faecalis, Bifidobacterium, Lactobacillus) were cultured; T cell subsets (CD4+, CD8+, Treg) by flow cytometry. Patients were stratified by median levels into high/low groups. Correlations and diagnostic efficacy were assessed using Pearson test and ROC (receiver operating characteristic) analysis. Baseline data were comparable among three groups. Fecal flora (E. coli, E. faecalis, Bifidobacterium, Lactobacillus) and T cells (CD4+, CD8+, regulatory T cells) differed significantly. Serum S100A12 and DAO were elevated in colon cancer versus benign/control groups. High/low subgroups showed disparities in flora and T cells. S100A12 and DAO positively correlated with E. coli/E. faecalis, CD8+ T, and Treg, but negatively with Bifidobacterium, Lactobacillus, and CD4+ T. The cancer group had reduced CD4+ and CD4+/CD8+ ratio, and elevated CD8+ and Treg. Combined S100A12+DAO detection outperformed single markers. Elevated serum S100A12 and DAO in colon cancer are associated with gut microbiota dysbiosis and immune dysregulation. Their combination shows promise as a potential biomarker for early diagnosis and disease evaluation. https://ijaai.tums.ac.ir/index.php/ijaai/article/view/4643 https://ijaai.tums.ac.ir/index.php/ijaai/article/download/4643/2350