Somatic Mutation Theory of Cancer

The somatic mutation theory of cancer holds that cancer originates from a stepwise accumulation of mutations arising in the DNA of somatic, or non-reproductive, cells, mutations that progressively disrupt the normal molecular controls governing cell division, allowing the affected cell line to proliferate uncontrollably and eventually form a tumor. Early foundational support for a chromosomal basis of cancer traces to the work of German biologist Theodor Boveri in the first years of the twentieth century, though the theory reached its modern molecular form gradually across the second half of the twentieth century as specific cancer-promoting genes, called oncogenes, and cancer-suppressing genes, called tumor suppressor genes, were identified and characterized. American physician Alfred Knudson made an especially influential contribution in a 1971 paper proposing his two-hit model, based on his statistical study of the childhood eye cancer retinoblastoma, showing that both copies of a tumor suppressor gene typically need to be inactivated by separate mutational events before cancer develops in a given cell lineage. The somatic mutation theory remains the dominant working framework in cancer biology, though it continues to be actively debated and refined against complementary or alternative models that emphasize other contributing factors, including broader chromosomal instability and the influence of a tumor's surrounding cellular environment.