Treatments should encourage healthy cells as well as killing unhealthy onesPhotograph: Agnes JonasIN THE POPULAR imagination, cancer starts with a mutation in the DNA of a normal cell. That mutation allows the cell to multiply uncontrollably, circumventing the body’s usual quality-control checks. Eventually, a tumour forms and breakaway cells spread to other parts of the body.Explore moreScience & technologyHealth careThe Economist todayHandpicked stories, in your inboxA daily newsletter with th...