“We are doing a sort of molecular archaeology,” says cancer geneticist Ludmil Alexandrov of Los Alamos National Laboratory in New Mexico, who led the analysis. While smoking’s link to cancer has been known for decades, “it’s always been a bit of a mystery why smoking increases the risk of cancers like bladder or kidney — tissues that aren’t exposed to smoke.”
Mutations in DNA arise naturally in a person’s lifetime, but some genetic changes — such as those spurred by smoking — increase the risk of certain cancers. Scientists have identified several patterns of DNA mutations that consistently show up in tissues of some cancers. These patterns, which may appear over and over again in a stretch of tumor DNA, can serve as a signature of the underlying mechanism that led to the mutations, offering clues to how different cancers strike.