Abstract P6-12-09: Association between cardiovascular risk factors and cardiac events among breast cancer patients enrolled in SWOG clinical trials
Authors: Hershman DL , Till C , Wright JD , Ramsey SD , Barlow WE , Unger JM 
Published: February 2018

Background: Due to early detection and improved treatments, women with breast cancer are living longer. Breast cancer shares risk factors with cardiovascular disease (CVD), and its treatments have adverse cardiovascular effects. Less is known about the association between cardiac risk factors and long-term cardiac events among the patients enrolled in breast cancer trials, as most trials fail to collect this information.

Methods: We examined the SWOG database to identify phase II/III breast cancer trials from 1999-2011. Among patients over 65 years, we linked the SWOG clinical records to Medicare claims data according to social security number and date of birth. This analysis included patients with 6+ months of Medicare coverage prior to baseline and 12+ months of Medicare coverage at any point after baseline. The comorbidities investigated at baseline were diabetes, hypertension, hypercholesterolemia, coronary artery/ischemic heart disease and obesity. A cardiac event was defined as an acute ischemic event or acute heart failure. Cox regression was used to calculate time-to-event, stratified by study ID and adjusted for baseline age, race, and prognostic risk score. Cox regression was performed separately for each CVD risk factor, and an additional analysis was performed to assess the impact of having multiple concurrent risk factors. Secondary analyses were performed separately by study type (Adjuvant, Advanced).

Results: Among patients linked to Medicare included in this cohort (N=742), the median age was 70, and median follow-up was 6 years. The majority of patients were non-Hispanic white. The most prevalent conditions were hypercholesterolemia (58%) and hypertension (73%). Only 13% had no baseline risk CVD factors. In a Cox regression, all baseline risk factors except hypercholesterolemia and obesity were statistically significantly or borderline statistically significantly associated with an increased risk of eventual cardiac event, and for ischemic heart disease the increased risk was more than two-fold (HR=2.27, 95% CI=1.46-3.54, p=0.0003) and for baseline diabetes nearly two-fold (HR=1.75, 95% CI=1.13-2.71, p=0.01). In addition, there was evidence of a linear association of number of concurrent risk factors and cardiac events (HR per additional risk factor = 1.35 (1.09-1.66), p=0.005). In the stratified analysis, the associations were statistically significant only for participants on adjuvant studies. No association between baseline cardiac risk factors and cardiovascular outcomes were seen among patients with advanced cancer.

Conclusions:In summary, we found that even among healthy breast cancer patients selected for clinical trials, baseline CVD risk factors are associated with an increased risk of cardiac events, however this association was not observed for patients with advanced disease, who are more likely to die from breast cancer before experiencing a cardiovascular event.

Citation Format: Hershman DL, Till C, Wright JD, Ramsey SD, Barlow WE, Unger JM. Association between cardiovascular risk factors and cardiac events among breast cancer patients enrolled in SWOG clinical trials [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P6-12-09.