At the end of experiment, a significant reduction of tumor volume and weight in CORM-3 treatment group was observed compared with the RuCl3 treatment group (Fig. 6D–F), indicating that CO exerts anti-tumor activity in vivo, which was also supported by the decrease of Ki-67 proliferative index after CORM-3 treatment (Fig. 6G, H). This evidence concerns the gene MKI67 and neoplasm.