The risk increases within five years of radiotherapy and remains increased for at least 20 years. The increase in risk is particularly pronounced for women with other heart disease risk factors, such as smoking, high BMI or diabetes, at time of radiotherapy.
It has always been assumed that radiotherapy for breast cancer increases the risk of heart disease later in life. However, little has been known about the nature of the risk and if certain individuals are particularly susceptible to ionising radiation. The present study by researchers at Karolinska Institutet and their colleagues from Denmark and Britain has addressed these issues.
The study included almost 2,200 Danish and Swedish women who had received radiotherapy for breast cancer between 1958 and 2001. Information from radiotherapy charts and medical records were used to estimate mean radiation dose to the heart. The researchers gathered information about the medical history and risk factors for heart disease of each woman.
A clear correlation between radiation dose and risk of ischemic heart disease was revealed. The risk was particularly pronounced for women with diabetes, chronic obstructive lung disorders, angina or other heart diseases, a high BMI, or who were smokers at time of their treatment. The highest risks were noted during the first ten years following treatment, after which the risk decreased, but was still elevated 20 years after radiotherapy.
The risk of a subsequent ischemic heart disease was influenced by age at therapy, previous disorders and heart dose. Comparing a 50 year old breast cancer patient without previous risk factors for heart disease and who did not receive radiotherapy, to a woman of similar age with hypertension and high radiation doses to the heart (10 Gy), reveals approximately 3 times higher risk of ischemic heart disease in the treated patient.
“The results confirm what we have long suspected, that irradiation increases the risk of myocardial infarction, and that women with other known risk factors for ischemic heart disease are more susceptible than others,” says Per Hall, Professor of radiation epidemiology at Karolinska Institutet’s Department of Medical Epidemiology and Biostatistics. “This gives us stronger grounds on which to weigh the pros of irradiation against the cons of its harmful effects on the heart for individual patients.”
Researchers from the following organizations took part in the study: University of Oxford, Royal Surrey County Hospital, and Surrey University, all three in the UK, Odense University Hospital, University of Southern Denmark, Aalborg University Hospital, and Rigshospitalet Copenhagen University Hospital, in Denmark, University of Southern Florida, US, Karolinska Institutet, and Karolinska University Hospital, Sweden. The study was made possible with funding under the EUs Radiation Associated Cardiovascular Events (RACE) project. The research team also received grants from the UK Department of Health, the British Heart Foundation, and Cancer Research UK.
Risk of Ischemic Heart Disease in Women Irradiated for Breast Cancer
New England Journal of Medicine, 14 March 2013