Cardiovascular disease incidence in women with early-onset breast cancer.

12018 Background: Early-onset breast cancer (BC) before age 40 is generally associated with advanced stage at diagnosis and worse outcomes. Improvements in detection and treatment have led to reduction in BC mortality. Cardiovascular disease (CVD) is the leading cause of non-BC death in women with BC, but younger women are traditionally considered to be at lower risk for CVD. Given the limited data on CVD in early-onset BC, this study evaluates incident CVD in women younger than age 40 in the Pathways Heart Study. Methods: The Pathways Heart Study (R01/U01CA214057) is an ongoing, prospective cohort study including 14,402 women diagnosed with BC at KPNC from 2005-2013 and followed through 2021. In this study, eligible BC cases were women age 18-39 years at time of stage I-III BC diagnosis without pre-existing CVD. Cases were matched 1:5 to controls without BC on age at diagnosis and race/ethnicity. Cancer treatment, CVD (ischemic heart disease, heart failure, cardiomyopathy, stroke) and cardiometabolic risk factors (hypertension, diabetes, hyperlipidemia) were extracted from electronic health records. Cumulative incidence rates (CIR) were calculated as number of incident CVD events divided by total person-time at risk and expressed per 1,000 person-years. Results: A total of 535 women with early-onset BC were matched to 2,651 controls. Mean age was 35.1 years with mean follow up of 7.8 years. Overall, cases had a higher CIR of CVD (3.40 per 1,000 person-years (PY)) than controls (1.37/1000 PY). CIRs of hypertension, dyslipidemia, and diabetes were higher in cases compared to controls (14.89, 12.14, and 9.74/1000 PY, respectively). Among BC types and stage, women with hormone receptor-positive HER2-positive and stage III BC had the highest CVD CIRs (7.14 and 5.65/1000 PY, respectively). Women who received chemotherapy with anthracyclines and those who received endocrine therapy had higher CVD CIRs compared with those who did not, while there were no differences by receipt of radiation therapy (Table 1). Conclusions: Although the absolute incidence of CVD was low in BC patients younger than 40 years, these patients experienced a >2 fold higher CVD rate compared with matched controls. Patients treated with anthracyclines and endocrine therapy had higher CIR of CVD compared with those not treated. Future analyses will include formal comparison through survival and regression models of incident CVD and cardiometabolic disease in women with early-onset BC, accounting for confounders, including treatments received, education, income, and comorbidities. Cumulative incidence rates (CIR) of cardiovascular disease (CVD) in women age <40 years in the Pathways Heart Study. CIR of CVD per 1,000 person-years (95% CI) Chemotherapy With Anthracycline 4.15 (2.07, 7.43) Without Anthracycline 3.39 (0.70, 9.89) None 0.00 (0.00, 6.31) Endocrine Therapy Yes 3.77 (1.88, 6.74) No 2.50 (0.51, 7.29) Radiation Therapy Yes 3.40 (1.55, 6.45) No 3.40 (1.10, 7.93)