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Knudson's two-hit hypothesis. (Top) Semilogarithmic plot of fraction of retinoblastoma cases not yet diagnosed versus age of patient. (Bottom) Model of events in hereditary versus sporadic retinoblastoma. (Top, Reprinted from Knudson AG. 1971. Proc Natl Acad Sci 68: 820–823, Fig. 1, p. 823.)
