In a hospital west of Shanghai, Wu Shixiu since March has been trying to treat cancer patients using a promising new gene-editing tool. U.S. scientists helped devise the tool, known as Crispr-Cas9, which has captured global attention since a 2012 report said it can be used to edit DNA. Doctors haven’t been allowed to use it in human trials in America. That isn’t the case for Dr. Wu and others in China. In a quirk of the globalized technology arena, Dr. Wu can forge ahead with the tool because he faces few regulatory hurdles to testing it on humans. His hospital’s review board took just an afternoon to sign off on his trial. He didn’t need national regulators’ approval and has few reporting requirements.