The Risk of Cancer-Associated and Radiotherapy-Associated Cardiovascular Diseases among Patients with Breast Cancer.

Background: The cardio-related issues should be emphasized as the survival rates of breast cancer increased. We investigated the risk of coronary artery disease (CAD) and stroke due to breast cancer or radiotherapy.
Methods: In this retrospective cohort study, breast cancer patients diagnosed between 2007 and 2016 were recruited from Taiwan Cancer Registry Database and were followed until the end of 2018 by linking with the Taiwan National Health Insurance Database. The general population was randomly selected from the whole population in 2007. Standardized incidence ratios (SIR) were calculated to compare the risk of CAD and stroke between patients and the general population. Within the cohort, we included the patients diagnosed between 2011 and 2016. Cox proportional hazards model and subdistribution hazard function were used to investigate the associations of radiotherapy with the risk of CAD and stroke.
Results: Overall SIR of CAD was 0.82 (95% confidence interval [CI]: 0.78-0.86), while were 1.43 and 1.08 (95% CI: 1.30-1.55 and 1.00-1.16) 1 and 2 years after diagnosis, respectively. Overall SIR of stroke was 0.63 (95% CI: 0.60-0.67), the results were similar after considering the time since diagnosis. The adjusted hazard ratios (HR) for the associations of radiotherapy with CAD and stroke risk were 0.91 (95% [CI] = 0.76-1.09) and 0.84 (95% CI = 0.68-1.04), respectively. The results were similar by using subdistribution hazard function.
Conclusions: The risk of CAD was higher within the first 2 years of breast cancer diagnosis. We found no association between radiotherapy and the risk of CAD and stroke.
Competing Interests: Disclosure This work was supported by the Health Promotion Administration, Ministry of Health and Welfare (grant no. A1091115): Tobacco Health and Welfare Taxation. The content of this research may not represent the opinion of the Health Promotion Administration, Ministry of Health and Welfare. The funders had no role in study design, data collection and analysis, the decision to publish, or preparation of the manuscript. The authors have no conflict of interest to declare.
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