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

In the present retrospective cohort study, we investigated CAD and stroke risk due to breast cancer and radiotherapy. Compared with general population, the risk of CAD was higher within the first 2 years of breast cancer diagnosis, while the risk was lower for stroke. There is no association between radiotherapy and the risk of CAD and stroke. 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.