The establishment of effective preemptive medicine against cancer is a very important issue. Now that the public is more likely to face the risk of cancer, with the era of genome medicine it is necessary to establish cancer chemopreventive agents as drugs as one of the active cancer prevention methods. To date, large clinical trials using cancer chemopreventive agents have yielded a limited number of beneficial results, and only tamoxifen and raloxifene have been approved as cancer-preventive drugs. To date, the mechanism of carcinogenesis has been thoroughly revealed, and the development of cancer chemopreventive agents is being promoted through screening in line with the mechanism. There are still many points that need to be resolved in both animal experiments and clinical trials. This paper will introduce recent issues from the latest studies. Now, the infrastructure for clinical trials, which has been considered a bottleneck for the development of cancer chemopreventive agents, is being developed in Japan, so that we can address real preemptive medicine for cancer prevention.