Assessment of coronary heart disease morbidity and mortality after radiation therapy for early breast cancer

PURPOSE: To assess the risk of fatal and nonfatal myocardial infarction (MI) after breast-conserving surgery (BCS) and radiation therapy (RT) for left-sided breast cancer. PATIENTS AND METHODS: A hospital-based retrospective cohort linkage study of all breast cancer patients registered at the Princess Margaret Hospital (PMH), Toronto, Canada, between 1982 and 1988 who were treated with postlumpectomy RT was performed. Available identifiers for the study cohort were linked to two province-wide health files: the Canadian Institute for Health Information Hospitalization File and the Ontario Mortality Database. Admissions to hospital for MI and deaths attributable to MI were identified. The relevant original health records were abstracted to verify the diagnosis of MI according to diagnostic criteria used in the World Health Organization multinational monitoring of trends and determinants in cardiovascular disease (MONICA) project. We compared incidence of MI in the study cohort with the general population and incidence of MI after therapy for left- versus right-sided breast cancer. RESULTS: A cohort of 2,128 patients was identified. The median length of follow-up was 10.2 years. The incidence of MI in the study cohort was comparable to that in an age-matched general population of women in Ontario. There were 70 coronary events among 56 patients after breast irradiation. According to MONICA criteria, 53 and six events were characterized as definite and possible MIs, respectively. Eleven events did not satisfy MONICA criteria for MI. Twenty-six patients treated for left-sided and 23 patients treated for right-sided breast cancer experienced at least one definite or possible MI (log-rank test, P = .66). There were eight fatal MIs among the left-sided group and six among the right-sided group. There was no excess of other cardiac diseases among patients who received left-sided radiotherapy compared to the right-sided group. CONCLUSION: We have found no evidence for excess morbidity and mortality from coronary artery disease among women treated with RT to the left breast after BCS at 10.2 years of follow-up. Longer follow-up is required to confirm that excess cardiac disease has been completely avoided.