Abstract. Interleukin-6 (IL-6) is a well-known etiological factor of colitis-associated colorectal cancer (CAC) and has a significant role in CAC progression. In addition, hypoxia‐induc- ible factor 1α (HIF-1α) serves a primary role in the progression

Interleukin-6 (IL-6) is a well-known etiological factor of colitis-associated colorectal cancer (CAC) and has a significant role in CAC progression. In addition, hypoxia‐inducible factor 1α (HIF-1α) serves a primary role in the progression of CAC. However, the association between IL‐6 and HIF‐1α during the progression of CAC remains unclear. To investigate this association, the present study induced CAC in a mouse model using azoxymethane and dextran sulfate sodium. In addition, an anti‐IL‐6 receptor antibody was used to inhibit IL‐6. In this model, anti‐IL‐6 receptor antibody treatment significantly inhibited the development of CAC and the expression of HIF-1α, in colorectal adenomas and adenocarcinomas. In patients with CAC, the HIF‐1α gene was demonstrated to be overexpressed in tumor tissue compared with adjacent non‐malignant tissue. Furthermore, HIF‐1α mRNA expression was positively correlated with serum IL‐6 concentration. The results of the present study suggest that IL‐6 promotes CAC progression, in the early stage of the disease, through HIF‐1α regulation.