Peyton Rous won the 1966 Nobel Prize in Physiology or Medicine for his discovery of tumor-inducing viruses.
In 1911, Rous reported that a filtered extract from a chicken sarcoma could transmit the disease to healthy chickens. The finding showed that a virus, rather than only a transplanted mass of cells, could cause cancer in animals.
The virus became known as Rous sarcoma virus. At first, many researchers doubted that viruses could be responsible for tumors, so the importance of the discovery was recognized only gradually.
Rous shared the 1966 prize with Charles Huggins, whose separate work concerned hormonal treatment of prostate cancer. Later research on Rous sarcoma virus helped reveal oncogenes, genes that can contribute to uncontrolled cell growth when altered or misregulated.