Radiation-related heart disease after breast cancer radiation therapy in Korean women

Purpose: To study the late cardiac toxicity of breast radiation therapy (RT) in Asian women. Methods: Female breast cancer patients in Korea who underwent breast conservation surgery followed by RT from 1990–2012 were identified from two large registries at institution and population levels. Cumulative incidences of acute coronary events (ACE) or cardiac mortality were estimated in relation to the laterality of breast cancer using a competing risks analysis. Results: In an analysis of 2577 women from a single institution, 3.7% were obese (body mass index ≥30), and 3.4% were ever-smokers. Patients with a history of hypertension, diabetes, or coronary artery disease were 17.5, 5.7, and 2.8%, respectively. The mean heart doses were 6.2 and 1.5 Gy for left- and right-sided tumors, respectively. With a median follow-up of 7 (range 1–23) years, the overall and breast cancer-specific survivals at 10 years were 94.9 and 96.5%, respectively. The 10-year cumulative incidence of ACE was 2.96%. The mean time to ACE was 5.2 ± 3.9 years (range 1–17). There was no clinically relevant difference in rates of ACE between left-sided and right-sided patients, with an adjusted hazard ratio of 1.16 (CI 0.59–2.29). An analysis of 24,235 women in a nationwide registry validated these negative findings with respect to cardiac mortality, with an adjusted hazard ratio of 1.52 (CI 0.37–6.25). Increasing age, a higher body mass index, and a history of hypertension or ischemic heart disease were identified as risk factors. Conclusions: Our findings reassure that excess risk from breast RT may be small in healthy women, most of who not smoke, weigh less, and have fewer risk factors. A validation using a larger data set of National Health Insurance Corporation is ongoing.