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

The p53 tumor suppressor was first identified as a cellular protein that bound to the large T antigen in SV40-transformed cells. Initially thought to be the product of an oncogene, p53 turned out to be an anticancer protein whose loss or mutation could promote tumorigenesis. Subsequent work revealed it functions as a DNA-binding transcription factor central to the DNA damage response and cell cycle control. In this excerpt from his forthcoming book on the history of cancer research, Joe Lipsick looks back at the discovery of p53 and the groundbreaking work that revealed its role as “guardian of the genome.”