Joseph Lipsick Departments of Pathology, Genetics, and Biology, Stanford University, Stanford, California 94305-5324, USA Correspondence: lipsickstanford.edu

The discovery and characterization of retroviral oncogenes were important milestones in cancer research. The viruses turned out not to be key causes of cancer in humans, but the oncogenes they carried provided key clues to the role cellular genes, the proto-oncogene counterparts of these sequences, played in tumorigenesis. In this excerpt from his forthcoming book, Joe Lipsick looks back at early work on retroviruses, such as the experiments that distinguished their ability to infect and transform cells, the groundbreaking work on Src, and some of the controversy surrounding the Nobel Prize awarded for these discoveries.