— People who receive stem cell transplants for diseases such as leukaemia appear to face a higher risk of developing secondary cancers, especially if the cells come from a female donor, according to a preliminary study.
The scientists behind the new report caution that future stem cell treatments for ailments such as spinal cord injury and heart failure might also carry a cancer risk. However, experts point out that the study is far from conclusive and more work needs to be done to confirm a link between stem cell transplants and tumours.
Donna Forrest of the British Columbia Cancer Agency in Canada, and colleagues, reviewed the medical records of more than 900 adult patients who had received haematopoietic stem cell transplants, also known as bone marrow transplants, in the past two decades. The vast majority of these transplant recipients were suffering from leukaemia.
Of the patients included in the study, 28 developed secondary tumours such as skin, lung or breast cancer within 10 years of receiving the stem cell transplant. After Forrest and her colleagues had excluded some of these cancers from their analysis due to incomplete reporting, they found that the remaining patients faced a 2.3% risk of cancer over the course of 10 years nearly twice the risk in the general population.
The analysis also revealed that patients who received stem cell transplants from female donors had an even higher risk of developing a secondary tumour. Their risk of developing cancer over the course of 10 years was 4.6%, while patients given stem cells from a male donor had a 1.8% risk.
Men who received stem cells from female donors had more than twice the risk of developing cancer compared with women who received the same.
This is the first study to demonstrate that stem cells from women carry a greater cancer risk than those from men, Forrest says. She suggests that the cells from female donors many of whom have had children might differ somehow. Their pregnancies might have made their cells more likely to be disruptive when transplanted into recipients. This in turn might have caused chronic inflammation in the patients, putting them at greater risk for cancer, she speculates.
Forrest adds that the findings are preliminary and that the analysis did not control for confounding factors, such as whether a patient smoked or maintained a healthy body weight. It therefore remains unclear exactly how much the stem cell transplants contributed to the risk of second cancers, she says.
Experts also caution that the drugs given following such transplants are known to put patients at greater risk of these secondary tumours. "The findings from this study are not surprising, explains Ed Yong at the London-based organisation Cancer Research UK. Cancer patients who undergo stem cell transplants are given very intensive treatments and immunosuppressive drugs, which make them more vulnerable to developing other cancers later on in life.
He stresses that the transplants helped save the leukaemia patients lives: "These treatments are only offered to patients with very poor long-term prognoses, or who have failed to respond to more conventional treatments. While this study indicates that stem cell transplants may carry an additional risk, they are only given to patients who have limited options.
Given the hope that stem cell transplants might one day help patients recover from numerous ailments ranging from spinal cord injury to heart failure more studies are necessary to find out whether such treatments might influence cancer risk, says Forrest.
There is a growing need to understand what happens to transplanted stem cells, says Simon Cherry, a researcher at the University of California, Davis, US, because they can develop into many different cell types and theres always the danger that something can go wrong. He says that researchers should actively investigate the possible cancer risk to avoid any unexpected negative outcomes of future trials involving stem cells.
Journal: Cancer (DOI: 10.1002/cncr.22375)