Don't worry yourselves to death even if those who have donated blood for you might have developed cancer since.
There is no evidence that recipients of blood from donors with undiagnosed cancer are any more or less likely to develop cancer than recipients given blood from non-cancer donors, a study of more than 350,000 blood transfusion recipients shows.
Researchers say the findings are reassuring and a major advancement in the understanding of long-term transfusion-related risks.
"Continuous attention to transfusion safety has reduced the risk of transfusion-transmitted disease to a current record low," writes researcher Gustaf Edgren of the Karolinska Institutet in Stockholm, Sweden, and colleagues.
Although most infections and complications have been relatively easy to identify, the possible transmission of chronic diseases with unknown causes has been far more difficult to address, they write.
The study analyzed data gathered between 1968 and 2002 from computerized blood bank registers in Denmark and Sweden, including information on 1.13 million blood donors and 1.31 million blood transfusion recipients.
Out of the more than 350,000 recipients included in the final analysis, just over 12,000 (3%) were exposed to blood products from donors who later went on to develop cancer.
The blood transfusion recipients were followed for up to 34 years, and the results showed no increased risk of cancer associated with the exposure.
"Our data provide no evidence that blood transfusions from precancerous blood donors are associated with an increased risk of cancer among recipients compared with transfusions from non-cancerous donors," the researchers conclude.
Thanks to the scope and thoroughness of the study, experts say the results represent an important step forward in evaluating one of the potential long-term risks of blood transfusion. But much more is still unknown.
"Blood is an immensely complex and biologically active substance. Although the potential for standard allogeneic blood transfusion [from unknown persons] to save lives is incontrovertible, our understanding of the full consequences of transfusion is rudimentary," writes Garth Utter of the University of California, Davis, in a commentary that accompanies the study published in The Lancet.