People accumulate DNA mutations at very different rates, and that difference may help explain why some develop cancer, a new study suggests.

Researchers at City of Hope and TGen compared mutation counts in organs from healthy people and cancer patients. Cancer cells carried about four times as many DNA mutations as normal cells.

More surprisingly, healthy people varied widely. Some had up to eight times more mutations than others of the same age, the study found.

The team tested three explanations. The one that fit best, called the tail hypothesis, says people with higher mutation rates are more likely to develop cancer.

First author Sophie Penisson said understanding why mutation rates differ could change how doctors identify cancer risk.

Senior author Cristian Tomasetti said measuring a person’s mutation rate could one day guide personalised cancer prevention. The study was published in the journal Cancer Research. The findings could also help explain why cancer patients often carry more mutations in healthy tissue too.