Levine discovered the tumor suppressor protein p53, also known as Tumor protein P53. Because it prevents cancer formation TP 53 is classified as a tumor suppressor gene. The discovery was completed in 1989 and recorded in the following paper: Cathy A. Finlay, Philip W. Hinds, and Arnold J. Levine, "The p53 proto-onogene can act as a suppressor of transformation," Cell, 57 (1989), 1083-1093.