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Cancer geneticist whose insights launched the search for tumour-suppressor genes.
After years of observing children with the rare eye cancer retinoblastoma, Alfred Knudson proposed an explanation for how two different forms of it arise. His 'two-hit' hypothesis led to the realization that the loss of gene function, not just the activation of a cancer-causing gene, could cause cancer.
Knudson, who was born in Los Angeles, California, in 1922, died on 10 July, aged 93. After completing a bachelor of science degree at the California Institute of Technology (Caltech) in Pasadena in 1944, he earned a medical degree from Columbia University in New York City in 1947, and a PhD in biochemistry and genetics in 1956, also at Caltech. Knudson then spent years treating children in medical centres in California and New York.
During the 1950s and 1960s, cancer epidemiologists were preoccupied with trying to understand the environmental causes of the disease. In a 1953 paper, cancer biologist C. O. Nordling noted that in developed nations, the incidence of cancer seemed to increase with age (C. O. Nordling Br. J. Cancer 7, 68-72; 1953). Nordling's proposal that the occurrence of cancer needed the accumulation of at least six sequential mutations was ultimately proved wrong. But his idea that cancer is...