Long-Term Risk of Cardiovascular Disease in 10-Year Survivors of Breast Cancer

Background Radiotherapy for breast cancer as delivered in the 1970s has been associated with increased risk of cardiovascular disease, but recent studies of associations with modern regimens have been inconclusive. Few data on long-term cardiovascular disease risk according to specific radiation fields are available, and interaction with known cardiovascular risk factors has not been examined. Methods We studied treatment-specific incidence of cardiovascular disease in 4414 10-year survivors of breast cancer who were treated from 1970 through 1986. Risk of cardiovascular disease in these patients was compared with general population rates and evaluated in Cox proportional hazards regression models. All statistical tests were two-sided. Results After a median follow-up of 18 years, 942 cardiovascular events were observed (standardized incidence ratio = 1.30, 95% confidence interval [CI] = 1.22 to 1.38; corresponding to 62.9 excess cases per 10 000 patient-years). Breast irradiation only was not associated with increased risk of cardiovascular disease. However, radiotherapy to either the left or right side of the internal mammary chain was associated with increased cardiovascular disease risk for the treatment period 1970–1979 (for myocardial infarction, hazard ratio [HR] = 2.55, 95% CI = 1.55 to 4.19; P