Objective: In Japan, pharmaceutical manufacturers have been required to develop a Risk Management Plan (RMP) since April 2013. Publication of the RMP is expected to enable the wide content-sharing of post-marketing risk management and its utilization among medical professionals to further enhance and strengthen post-marketing safety measures. In this study, we examined what points should be focused on for continuous utilization of RMPs after drug approvals by investigating the numbers of safety concerns addition of antineoplastic and immunomodulating agents, and where safety concerns added after approval are listed in package inserts. Furthermore, we investigated the reasons why these safety concerns were considered as such. Methods: Antineoplastics and immunomodulating agents, which account for more than half of all drugs containing new active ingredients approved in recent years, among drugs containing new active ingredients approved from fiscal year (FY) 2013 to FY 2019 were included in the study. The safety concerns (excluding important missing information) in RMPs as of April 1, 2021 for the subject drugs were compared with those at the time of approval. Safety concerns added after approval were investigated where they were listed in package inserts as of April 1, 2021. Furthermore, risks that were added as important potential risks were investigated as to why they were considered as such. Results: There were 117 risks added after approval. Those added to the important identified risks were listed in one of the sections of the package insert, whereas 11 risks were added to the important potential risks that could not be confirmed in the package inserts. Some important potential risks added after approval are suspected to have a causal relationship with the drug, but were not listed in the package inserts. Conclusion: It is important to utilize RMPs continuously to further understand risks of taking the drug.