People with Down's syndrome may be less likely to need cancer treatment, researchers have claimed.
A study by scientists at Johns Hopkins University found that the additional copy of chromosome 21 carried by people with the genetic disorder appears to block the development of some forms of cancer.
Mice with a third copy of a chromosome were found to develop far fewer cancers and the number of copies of a particular gene, Ets2, seems to be related to the risk of developing tumours.
Roger Reeves, professor of physiology at the university, commented: "These results support studies concluding that people with Down's syndrome get fewer cancers of many types."
Cancer Research UK said that the relationship between Down's syndrome and cancer is "complex".
A spokesman for the charity told the BBC: "More research is needed to unravel this paradox if this discovery is to benefit cancer patients in the future."