All cancers are driven by genetic mutations that develop in a person's body cells over her or his lifetime. However, what causes these mutations is still largely unknown. Now, researchers have released the findings of a large-scale study that sheds light on these processes. Investigators analyzed the genetic makeup of 30 common cancers in thousands of patients and identified 21 patterns of mutation, or 'signatures,' underlying cancer development. All cancer types had at least two signatures, and some had up to six, reflecting the multiple influences that contribute to cancer. The researchers also uncovered the biological processes behind many of these signatures, such as aging or enzymes involved in fighting off virus infections.