There is a growing expectation for real world data(RWD)in the development of drugs and medical devices in oncology area. Current RWD in Japan consists of electronic medical record(EMR)and DPC data from hospital information systems, claims data for reimbursement, disease registry data by academia, and so on. The DPC database is now widely used as a commercial RWD, but our research has revealed that it has a limited number of data items available, which may pose a disadvantage in evaluating patient background and the efficacy and safety of drugs, although they are essential for cancer clinical research. On the other hand, Flatiron Health Inc.'s database in the US, which is RWD derived from EMR, allows for collecting essential information in oncology by installing a cancer-specific EMR system into participating hospitals as well as by deploying certified cancer experts who engage in building structured clinical data. In the use of cancer RWD, it is important to select databases based on the purpose of analysis and understand that the quality of databases varies.