High iron levels could be a reason why eating red meat raises the risk of bowel cancer, a study suggests.
Iron may interact with a faulty gene in the gut to trigger cancer, scientists said.
Red meat contains large amounts of iron and is also known to increase the likelihood of bowel cancer.
The discovery could lead to new cancer treatments that target iron in the bowel.
In studies of mice, researchers found that susceptibility to bowel cancer was strongly influenced both by iron and a gene called APC.
When the APC gene was faulty, mice with a high iron intake were two to three times more likely to develop the disease.
Mice fed a low-iron diet remained cancer free even if the gene was defective.
But when the APC functioned normally, high iron levels did no harm.
Lead scientist Professor Owen Sansom, deputy director of the Cancer Research UK Institute for Cancer Research in Glasgow, said: "We've made a huge step in understanding how bowel cancer develops.
"The APC gene is faulty in around eight out of 10 bowel cancers but until now we haven't known how this causes the disease.
"It's clear that iron is playing a critical role in controlling the development of bowel cancer in people with a faulty APC gene."