In March, 2017, the American Association for the Advancement of Science (AAAS) published a headline stating “Random errors in DNA replication play a major role in cancer”, referring to a new paper by Tomasetti and colleagues, 1 a follow-up to their first paper in 2015. Headlines subsequently appeared on many news and social media outlets reading “Most cancer cases arise from ‘ bad luck’” ( Scientific American) or “‘ Bad luck’ mutations increase cancer risk more than behavior, study says” ( CNN). Such a message, suggesting that cancers are largely due to bad luck, is an incorrect interpretation of the authors' results, and is ultimately misleading. We are concerned about the adverse effect this message might have on public health policies to prevent cancers. Here, we emphasise that mutations are a necessary but insufficient cause of cancer, and additional mechanisms (the hallmarks of cancer) are at work, including altered immune function.