Left Breast Radiation Therapy Doubles CV Disease Risk vs. Right Breast Radiation Therapy in Young Women
Women with left-sided breast cancer undergoing radiation therapy between 1985 and 2008 had over twice the risk of subsequent coronary artery disease (CAD) compared to women with right-sided breast cancer with up to 27.5 years of follow up, according to a study published Sept. 21 in JACC: CardioOncology.
Lauren E. Carlson, MPH, et al., studied participants in the Women’s Environmental Cancer and Radiation Epidemiology Study to evaluate the risk of CAD in breast cancer survivors. After excluding women who did not receive radiation therapy or who had a preexisting cardiovascular disease diagnosis, 972 women were eligible for analysis. All the participants were diagnosed with breast cancer between 1985 and 2008, were under 55 years old and had completed a cardiovascular health questionnaire. The average follow-up time was 14 years.
Results showed that participants had equal event-free survival of CAD for five years, regardless of breast cancer laterality. Women treated with left-sided radiation therapy had a smaller event-free survival portion for CAD at each subsequent five-year mark. In all, 46 participants reported a CAD diagnosis with 91% of diagnoses occurring more than five years after radiation therapy. Only 9% of CAD diagnoses were reported within the first five years of follow-up, demonstrating the need for long-term follow-up in younger breast cancer survivors according to the researchers.
In the study with up to 27.5 years of follow-up, the overall incidence of CAD for women who received left-sided radiation therapy was 10.5% compared to 5.8% for women who underwent right-sided radiation therapy. For women diagnosed between ages 25-39 years, those who received left-sided radiation therapy had a 5.9% incidence of CAD, while those receiving right-sided radiation therapy reported no CAD. Women who were diagnosed between ages 40-54 years experienced an 18.7% incidence of CAD after undergoing left-sided radiation therapy and 6.8% after undergoing right-sided radiation therapy.
When evaluating the presence or absence of two or more cardiovascular risk factors, such as increased body mass index, smoking, high blood pressure or high cholesterol, there was little evidence for differences in the association between left-sided radiation therapy and CAD.
“Our study adds to the growing evidence that left-sided radiation therapy is an independent risk factor for future heart disease after treatment for breast cancer,” said Gordon Watt, PhD, a study author. “It is important that clinicians caring for younger breast cancer patients communicate the importance of radiation therapy for breast cancer while explaining the need for long-term attention to the risk of heart disease, particularly for women receiving left-sided radiation therapy. Radiation therapy is an indispensable part of breast cancer care, and the good news for breast cancer patients is that modern techniques and computerized treatment planning have reduced the amount of radiation that reaches the heart, thereby reducing the risk of developing heart disease.”
In an accompanying editorial, James Bates, MD, Ming Hui Chen, MD, MMSc, FACC, and Louis S. Constine, MD, explain, “This study also reaffirms the role of prolonged surveillance for CAD in younger survivors. Give the latency between radiation exposure and development of cardiovascular events, it is important that young women who have received left breast radiation therapy be considered at higher risk over their lifetime.”
Keywords: Cardiotoxicity, Cholesterol, Heart Disease Risk Factors, Smoking, Hypertension, Radiation Injuries, Heart, Heart Diseases, Breast, Risk Factors, Body Mass Index, Progression-Free Survival, Cancer Survivors, Coronary Artery Disease, Breast Neoplasms, Cardiovascular Diseases, Unilateral Breast Neoplasms
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