Cancer patients are usually not accepted as blood donors, but it can happen that people with an undetected growth still donate. Researchers at Swedish medical university Karolinska Institutet have therefore studied whether cancer cells can be transferred via the blood and cause cancer in the recipient.

"The results, which have to be considered reliable, settle one of the few remaining questions surrounding the safety of blood transfusions," says Professor Olof Nyrén of the Department of Medical Epidemiology and Biostatistics and the leader of the project.

The study was carried out in collaboration with researchers at Statens Serum Institut in Copenhagen. Digital information on 1.13 million blood donors and 1.31 million transfusion recipients in Sweden and Denmark was gathered, allowing the scientists to identify over 12,000 patients who had received blood from donors who were diagnosed with cancer within five years of the transfusion.

The recipients were followed for as long as 34 using record linkage with the Swedish and Danish cancer and cause-of-death registers and other such data. The control group consisted of 342,000 patients who could be said with certainty to have not received blood from donors with latent cancer. The cancer risk of the two groups were compared using statistical methods, taking into account sex, age, place of residence, blood group, number of transfusions and time since the first transfusion.

The team found that the patients in the two comparison groups had exactly the same cancer risk. No matter how the data was analysed, there was no evidence to suggest that patients who had received blood from donors with a yet undiagnosed tumour ran a greater risk of developing cancer themselves.; Source: The Swedish Research Council