Ever since the first blood-forming stem cells were successfully transplanted into people with blood cancers more than 50 years ago, researchers have wondered whether they developed cancer-causing mutations. A unique study1 on the longest-lived transplant recipients and their donors has revealed that people who receive donor stem cells don’t seem to have an increased risk of developing such mutations.

The results are surprising but reassuring, says Michael Spencer Chapman, a haematologist at the Barts Cancer Institute in London.

“It’s fantastic news for people undergoing these therapies,” says Alejo Rodriguez-Fraticelli, a quantitative stem-cell biologist at the Institute for Research in Biomedicine in Barcelona, Spain.