Background: Drug development for rare diseases is challenging because it is difficult to obtain relevant data from very few patients. It must be informative to grasp current status of clinical trials for drug development in rare diseases. Objective: Clinical trials in rare diseases are to be outlined and compared among the US, EU and Japan. Method: ClinicalTrials.gov (NCT, National Clinical Trial), EU Clinical Trials Register (EUCTR) and the Japan Primary Registries Network (JPRN) were analyzed. Clinical trials involving information on rare diseases and drugs were extracted by text-mining, based on the diseases and drugs derived from Orphanet and DrugBank, respectively. Results: In total, 28,526 clinical trials were extracted, which studied 1,535 rare diseases and 1,539 drugs. NCT had the largest number of trials, involving 1,252 diseases and 1,332 drugs. EUCTR and JPRN also had registry-specific diseases (250 and 22, respectively) and drugs (172 and 29, respectively) that should not be missed. Among the 1,535 rare diseases, most diseases were studied in only a limited number of trials; 70% of diseases were studied in fewer than 10 trials, and 28% were studied in only one. Additionally, most studied rare diseases were cancer-related ones. Conclusion: This study has revealed the characteristics of the clinical trials in rare diseases among the US, EU and Japan. The number of trials for rare diseases was limited especially for non-cancerrelated ones. This information could contribute to drug development such as drug-repositioning in rare diseases.
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