After decades of descriptive studies, the biology of cancer is undergoing a real revolution: with genetic approaches, researchers have identified many of the cell deregulations likely to drive tumours. A treatment combining arsenic and retinoic acid targets the protein responsible for promyelocytic leukaemia. This treatment, which has cured virtually all patients, gives hope that the in-depth understanding of carcinogenesis mechanisms may lead to new therapeutic approaches that could be transposed to other cancers.