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Famed cancer theorist Dr. Alfred G. Knudson Jr. dies at 93

PHILADELPHIA (AP) — A scientist and cancer researcher famed for a groundbreaking theory of how cancer develops has died in Philadelphia after a long illness. Dr. Alfred G. Knudson Jr. was 93. The Oliver H. Blair Funeral Home says Knudson died Sunday at his home. Knudson had been on the staff of the Fox Chase Cancer Center since 1976. He was renowned for his two-hit hypothesis proposing that people with hereditary cancers inherit one damaged gene pair but develop cancer only if they develop a second hit, the loss of the good copy in the gene pair. People who develop nonhereditary forms of cancer must get both hits, meaning such cancers often occur later in life. Knudson also predicted the presence of cancer-fighting genes in cells, now called tumor suppressor genes.