The dossier on cancer researcher Wu Xifeng was thick with intrigue, if hardly the stuff of a spy thriller. It contained findings that she’d improperly shared confidential information and accepted a half-dozen advisory roles at medical institutions in China. She might have weathered those allegations, but for a larger aspersion that was far more problematic: she was branded an oncological double agent. In recent decades, cancer research has become increasingly globalised, with scientists around the world pooling data and ideas to jointly study a disease that kills almost 10 million people a year. International collaborations are an intrinsic part of...