Some people accumulate genetic mutations in their healthy tissues far faster than others, and that hidden rate may explain much of their cancer risk, a new study has found.

Researchers at TGen and City of Hope compared normal and cancerous tissue from seven organs — bladder, colon, esophagus, liver, lung, prostate and stomach — using hundreds of normal and thousands of cancer samples.

Cancer cells carried a median of more than four times as many mutations as healthy tissue. The team tested three explanations and found the “tail hypothesis” fit best: people whose healthy cells mutate faster are more likely to develop cancer.

“Even after accounting for age, some healthy people had up to eight times more mutations than others,” said lead author Sophie Pénisson. Understanding why mutations build up at very different rates could change how risk is identified.

“Measuring a person’s mutation rate could become a critical way to identify people at higher risk and develop more personalized strategies to prevent cancer,” said co-author Cristian Tomasetti. The findings were published in Cancer Research.