Cardiovascular disease mortality among breast cancer survivors in Puerto Rico: A population-based competing risk analysis

Purpose: Cardiovascular disease (CVD) is an increasingly important cause of death among breast cancer (BC) survivors, yet competing mortality risks remain understudied in Puerto Rico. This study estimated the cumulative incidence of BC-specific and CVD-specific mortality and identified associated risk factors among Puerto Rican BC survivors using competing risk methodology. Methods: Data were analyzed from 17,430 female BC patients recorded in the Puerto Rico Central Cancer Registry (2004-2019) who survived at least 1 year post-diagnosis and were followed through 2021. Deaths were categorized as BC- or CVD-related. Fine-Gray competing risk models estimated subdistribution hazard ratios (HRs) with 95% confidence intervals, stratified by age group (18-64, 65-79, 80+), to evaluate demographic and clinical correlates of BC and CVD mortality at 5, 10, and 15 years post-diagnosis. Results: Among 17,430 survivors, 6,881 (39.5%) died during follow-up. BC was the leading cause of death (3,636 deaths; 52.8%), while 470 (6.8%) were due to CVD. Median survival was longer among those who died from CVD (5.5 years (IQR: 3.1, 8.7)) than from BC (3.6 years (IQR: 2.2, 5.9)). By 15 years post-diagnosis, CVD had become a major competing risk: among women aged 80+, the cumulative incidence of CVD mortality reached 14.5% (95% CI: 9.3, 19.4), approaching the BC mortality risk of 16.6% (95% CI: 12.4, 20.6). In younger survivors (ages 18-64), comorbidity significantly increased CVD mortality risk (HR=2.7, 95% CI: 1.5, 4.8) but was not associated with BC mortality (HR=1.0, 95% CI: 0.9, 1.2). Advanced stage and aggressive treatment modalities were consistently associated with greater BC mortality across age groups, while comorbidity and older age were key drivers of CVD mortality. Conclusions: While BC remains the primary cause of death among survivors, CVD emerges as a substantial competing risk, especially in older women with extended survivorship. Distinct risk profiles, such as the strong influence of comorbidities on CVD mortality in younger survivors and the narrowing difference between BC and CVD mortality in the 80+ age group, underscore the need for survivorship care models that integrate cancer surveillance and cardiovascular management.