Data Validation and Verification Using Blockchain in a Clinical Trial for Breast Cancer: Regulatory Sandbox[J] JOURNAL OF MEDICAL INTERNET RESEARCH 2020(22) Hirano, Tomonobu Motohashi, Tomomitsu Okumura, Kosuke Takajo, Kentaro Kuroki, Taiyo Ichikawa, Daisuke Matsuoka, Yutaka Ochi, Eisuke Ueno, Taro