Within the human genome, small DNA elements called retrotransposons have the potential to wreak mutational havoc by copying themselves and reinserting into the genome at multiple locations. Normal adult cells have suppressive mechanisms to stop these elements from jumping about, but according to a report published today (June 28) in Science, those mechanisms can break down in certain cancers. The findings suggest that, in some cases, jumping genes might even cause cancer or contribute to its progression

 “The paper is very important,” said Keith Slotkin a molecular geneticist at Ohio State University in Columbus, who did not participate in the study. “There has long been a weak association between cancer and transposable element activity, but this paper now categorically shows that transposable element activation is a source of new mutations in cancer cells.”

Retrotransposons are common in eukaryotic genomes and, thanks to repeated rounds of copying and inserting themselves over the course of evolution, they generally comprise a significant fraction of a species’ DNA. Indeed, they make up a whopping 45 percent of the human genome.

“Most are molecular fossils—dead pieces of DNA,” explained John Moran a human geneticist at the University of Michigan Medical School in Ann Arbor, who did not participate in the research. That is, they have accumulated so many mutations over the course of evolution that they are now merely inactive remnants. “But,” he said, “Some are actively mobilizing.