A new study published in the New England Journal of Medicine offers the best look yet at the increased risk for heart disease produced by radiotherapy for breast cancer. Further, this increased risk may just be the tip of the iceberg of more radiation-related problems, warns a cardio-oncologist in an accompanying editorial.
The new study, based on data from Sweden and Denmark of women treated with radiotherapy for invasive breast cancer, found a linear increase in the rate of heart disease associated with the dose of radiation received by the heart. Starting 5 years after radiotherapy, and with no sign of a threshold, the risk for major coronary events increased by 7.4% per gray. The mean dose of radiation was 4 Gy. Although the relative risk was consistent throughout the study, the increase in absolute risk was greatest in women with cardiac risk factors or established heart disease.
Findings from the study, according to the authors, “make it possible to estimate” a patient’s risk for heart disease related to radiation. “This absolute risk can be weighed against the probable absolute reduction in her risk of recurrence or death from breast cancer that would be achieved with radiotherapy.” The authors estimated that for a 50-year-old woman without preexisting risk factors and with a mean radiation exposure of 3 Gy, her risk for death from ischemic heart disease by age 80 would rise from 1.9% to 2.4% and her risk for an acute coronary event would rise from 4.5% to 5.4%. The risk for death by age 80 for an otherwise similar woman with existing risk factors would rise from 3.4% to 4.1%. Women exposed to larger doses of radiation would be exposed to even greater risks.
In the accompanying editorial, Javid Moslehi writes that results of the study suggest that “cardiac risk factors should be assessed and aggressively managed — starting at the time of radiation treatment (or even before) and continuing throughout survivorship.” To make matters worse, the findings “may represent just the tip of the iceberg.” Radiation may also cause increases in pericardial disease, peripheral vascular disease, cardiomyopathy, valvular dysfunction, and arrhythmias, according to Moslehi, and other breast cancer therapies, such as anthracyclines and hormonal therapies, may have “additional cardiotoxic effects.”
Moslehi, who is in the Cardio-Oncology Program at the Dana–Farber Cancer Institute, writes about the emerging new discipline of “cardio-oncology”:
Given the widespread use of radiation therapy in the treatment of breast cancer, and the continually expanding arsenal of novel therapies, the current study calls for greater collaboration between oncologists and cardiologists. An important lesson for the oncologist may be that the time to address concerns about cardiovascular “survivorship” is at the time of cancer diagnosis and before treatment rather than after completion of therapy. Similarly, cardiologists need to assess prior exposure to radiation therapy as a significant cardiovascular risk factor in survivors of breast cancer.