Modern-era radiotherapy and ischaemic heart disease-related mortality outcomes in Asian breast-cancer patients.

Introduction: Left-sided breast-cancer patients treated with adjuvant radiotherapy (RT) before the 1990s were associated with increased risk of cardiac mortality. Modern RT techniques have since improved, resulting in lower radiation doses to the heart. However, concerns regarding cardiac toxicity remain. In a retrospective cohort study, we compare the ischaemic heart disease (IHD)-related mortality of left-sided versus right-sided breast-cancer patients. We present the results of the cardiac mortality and all-cause mortality risk of Asian breast-cancer survivors treated with RT in Singapore. Material and methods: A total of 14,419 Asian women from a single institution were treated for breast cancer from 2000 to 2016. A systematic mortality follow-up was conducted until December 2015. The effect of breast cancer laterality on IHD-related mortality and on overall mortality was investigated. Mean heart doses were recorded for patients from 2010-2016. Results: In the irradiated group (n = 9556), we found no difference in IHD-related mortality or overall mortality when comparing the left- and right-sided breast cancers. The hazard ratio of cardiac mortality for left-sided versus right-sided RT was 0.94 (95% CI: 0.64-1.38). The hazard ratio for all-cause mortality was 1.03 (95% CI: 0.94-1.13). Conclusions: Our study of Asian cancer patients did not reveal a significant increase in the risk of IHD-related mortality or overall mortality comparing left- vs. right-sided breast cancers in modern-era RT.