Cardiac Morbidity of Adjuvant Radiotherapy for Breast Cancer
Journal of Clinical Oncology, Vol 23, No 30 (October 20), 2005: pp. 7475-7482
PURPOSE: Adjuvant breast irradiation has been associated with an increase in cardiac mortality, because left-sided breast radiation can produce cardiac damage. The purpose of this study was to determine whether modern adjuvant radiotherapy is associated with increased risk of cardiac morbidity.
PATIENTS AND METHODS: Data from the Surveillance, Epidemiology, and End Results–Medicare database were used for women who were diagnosed with nonmetastatic breast cancer from 1986 to 1993, had known disease laterality, underwent breast surgery, and received adjuvant radiotherapy.
RESULTS: Eight thousand three hundred sixty-three patients had left-sided breast cancer, and 7,907 had right-sided breast cancer. Mean follow-up was 9.5 years (range, 0 to 15 years). There were no significant differences in patients with left- versus right-sided cancers for hospitalization for ischemic heart disease (9.9% v 9.7%), valvular heart disease (2.9% v 2.8%), conduction abnormalities (9.7% v 9.6%), or heart failure (9.7% v 9.7%). The adjusted hazard ratio for left- versus right-sided breast cancer was 1.05 (95% CI, 0.94 to 1.16) for ischemic heart disease, 1.07 (95% CI, 0.89 to 1.30) for valvular heart disease, 1.07 (95% CI, 0.96 to 1.19) for conduction abnormalities, and 1.05 (95% CI, 0.95 to 1.17) for heart failure.
CONCLUSION: With up to 15 years of follow-up there were no significant differences in cardiac morbidity after radiation for left- versus right-sided breast cancer.
We had the advantage of a large population-based cohort of patients with complete billing records of all inpatient care. The size of our study population gave us adequate power to detect a relatively small (10%) increase in cardiac risk. In addition, by looking at cardiac morbidity we have a more sensitive and earlier predictor of cardiac damage than mortality. We also were able to analyze a variety of cardiac end points including ischemic heart disease, valvular heart disease, heart failure, and conduction disturbances. Finally, because our enrollment began with patients diagnosed in 1986, our data are more reflective of the modern radiation techniques than other studies have been previously.
In conclusion, in this study we found no significant differences in cardiac morbidity for left- versus right-sided breast cancer. These data are reassuring and suggest that modern adjuvant radiotherapy is not causing substantial clinically relevant cardiac disease. By making adjuvant radiotherapy a safer process, women can feel more confident about their treatment for breast cancer and their decision for breast-conserving surgery.