Embryonic stem cells, the controversial and versatile cells that seem able to do just about anything, have now expanded their repertoire into cancer prevention. A vaccine made from these cells shields mice against developing lung cancer under conditions thought to mimic the effects of smoking. Safety concerns about injecting stem cells into humans mean that regulatory agencies are unlikely to approve human tests of the vaccine, says lead researcher John Eaton at the University of Louisville in Kentucky. Nevertheless, he thinks the vaccine is worth testing in people at high risk of developing cancer, such as heavy smokers or people...