In this study, we showed that the expression levels of CCL7 were decreased in MC38 cells cultured with high glucose concentrations, the number of tumor-infiltrating CD11c+ cells decreased in STZ-induced diabetic mice, and that CCR1 and 2 were expressed on tumor-infiltrating CD11c+ cells, which may be another mechanism involved in the reduced anti-tumor efficacy of anti-PD-1 antibody in this model. The gene discussed is CCR1; the disease is neoplasm.