Normal somatic cells (e.g., lung, breast, or prostate) sustain DNA damage. If the rate of DNA injury exceeds the rate of repair, then random genes become mutated. A chance mutation in a gene controlling growth (oncogenes or tumor suppressor genes) causes exuberant and sustained growth. This is an important first step toward cancerous transformation, but not the only one, because growth represents only one of many hallmarks of cancer. Other gene mutations accumulate randomly over time. When certain critical abilities (hallmarks) coalesce, the cell fully transforms into a cancer.
