Debra L. Beck, MSc, and Eugene Braunwald, MD

About 47% of women with stage I or II breast cancer received radiation therapy (RT). However, RT increases the risk of coronary artery disease (CAD), with those treated for a left-sided breast cancer receiving greater heart radiation than those treated for a right-sided breast cancer.  

Carlson et al sought to assess the risk of radiation-associated CAD specifically among younger breast cancer survivors (n=972) who were participants in the Women’s Environmental Cancer and Radiation Epidemiology (WECARE) study, a population-based study of women diagnosed with stage I or II invasive breast cancer before 55 years of age between 1985 and 2008.  

Participants were those who received RT, had no pre-existing cardiovascular disease diagnosis, and completed a cardiovascular health questionnaire.  

The researchers calculated the risk of radiation-associated CAD by comparing women treated with left-sided RT with women treated with right-sided RT using multivariable Cox proportional hazards models. 

A total of 46 participants reported a CAD diagnosis, and 91% of CAD diagnoses occurred more than 5 years after RT. Over a median follow-up of 14 years (range, 1-29 years), the 27.5-year cumulative incidences of CAD for women receiving left- vs right-sided RT were 10.5% and 5.8%, respectively (p=0.010; HR of CAD for left- vs right-sided RT, 2.5).  

There was no statistically significant effect modification by any factor evaluated, including by receipt of chemotherapy, hormone therapy for breast cancer, or anthracycline exposure.  

Summary 

The investigators concluded that, after RT for left-sided breast cancer, women had a 2.5-fold increased risk of CAD compared with women who received RT for right-sided breast cancer. “Laterality of RT is independently associated with an increased risk of CAD and should be considered in survivorship care of younger breast cancer patients,” wrote the authors.  

Comments 

In an editorial, Dr. Bates et al noted that modern RT techniques have likely altered the risk of CAD in breast cancer survivors, including simpler ones like breath-holding maneuvers during RT to displace the left heart caudally and out of the RT field in most women. Further collaboration between radiation therapists and cardiologists will further define the risk of RT for women and how to best screen for and limit the risk of CAD in survivors.  

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