By confirming the presence of a cancer virus, the hope and expectation was that a cancer vaccine would soon be on the horizon. Meanwhile, Gye’s painstaking research led him to propose a two-factor theory of cancer, which he described in The Lancet in 1925. When William Ewart Gye inoculated young chicks with both the cancer virus and an extract from the tumor, the chick would reliably develop cancerous tumors. Image: Popular Science, October 2025 issueHow cancer research today builds on Gye and Barnard’s workGye’s two-factor theory wasn’t entirely correct, but it pointed cancer researchers in the right direction. Instead of hunting for a single germ, modern cancer researchers point their powerful lenses on the internal machinery of cells.