“”” Stewart’s search for a viral basis for cancer wasn’t unprecedented. In 1911, virologist Peyton Rous discovered the Rous sarcoma virus, which he concluded co

“”” Stewart’s search for a viral basis for cancer wasn’t unprecedented. In 1911, virologist Peyton Rous discovered the Rous sarcoma virus, which he concluded could transmit cancer in chickens. In 1933, Richard Shope, a physician and virologist, discovered the Shope papilloma virus, which caused keratinous carcinomas in rabbits, and three years later, biologist John Bittner demonstrated that the mouse mammary tumor virus could be transmitted from a mother mouse to her young through her milk. But it was Ludwig Gross’s work on leukemia in mice in the 1950s that would lead to the first major breakthrough in the virus-cancer link—and it was that work that Stewart took up when she moved to the NCI in 1951. “””