Exposure to ionizing radiation during radiation therapy for breast cancer may increase the risk of heart attack or heart disease later in life, according to the results of a study published in the New England Journal of Medicine.
Many women with breast cancer are treated with breast-conserving surgery (lumpectomy) followed by radiation therapy in order to reduce the risk of cancer recurrence. Radiation therapy for breast cancer often involves some incidental exposure of the heart to ionizing radiation—and the risks of this exposure have been unclear.
Researchers conducted a population-based, case-control study of 2,168 women who underwent radiation therapy for breast cancer between 1958 and 2001 in Sweden and Denmark. The analysis indicated that 963 women had major coronary events such as heart attack, surgery to clear a blocked artery, or death from ischemic heart disease. These women were compared to the 1,205 women without major coronary events.
The results indicated that the risk for a major coronary event grew in direct proportion to the dose of radiation. A unit of radiation is known as a “gray”. For every gray, the risk of a major coronary event rose by 7.4 percentage points. The average dose that women in the study received was 4.9 gray, which translates to an increased risk of 36 percent for a heart event. The women with the highest exposure (an average of 15.8 gray) had a 116 percent increased risk of heart events, which is slightly more than double the normal risk. Women treated for a tumor in the left breast had a higher risk of heart problems because of proximity since the heart is located slightly to the left.
The risk of coronary events after radiation begins within a few years after exposure and continues for at least 20 years. Women with preexisting cardiac risk factors have greater absolute increases in risk from radiation therapy than other women.
The researchers note that the increased risk associated with radiation should not necessarily be cause for alarm. To put it into context, a healthy 50-year-old woman has a 1.9 percent chance of developing ischemic heart disease by the age of 80. If that same women is exposed to three gray of radiation, her risk increases by 22 percent—putting it at 2.4 percent, which is still quite small. What’s more—average radiation exposure is lower today (between one and five gray).
The researchers concluded that ionizing radiation for breast cancer can increase the risk of ischemic heart disease. Women who are already at an increased risk of heart disease may want to discuss alternative radiation techniques with their doctors.
Darby SC, Ewertz M, McGale P, et al. Risk of Ischemic Heart Disease in Women after Radiotherapy for Breast Cancer. New England Journal of Medicine. 2013; 368: 987-998.
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