Abstract
Historically, breast cancer patients with obesity have been more likely than normal-weight patients to receive dose-reduced chemotherapy, although contemporary dosing practices of patients with obesity remain unclear. Among 9708 women treated with adjuvant chemotherapy for stage I-IIIA breast cancer at two integrated healthcare delivery systems (2005-2019), we used generalized linear models to estimate adjusted prevalence ratios between body mass index (BMI) and comorbidity and chemotherapy dosing (first cycle dose reduction (FCDR), dose proportion < 90%) and average relative dose intensity (ARDI) < 90%). A strong, independent association was observed between BMI and FCDR (PR(BMI:40+ vs 18.5-<25): 9.74; 95% CI: 7.43-12.8; p-trend < 0.001) and ARDI < 90% (PR(BMI:40+ vs 18.5-<25): 2.69; 95% CI: 2.35-3.09; p-trend < 0.001). This association weakened over time, although remained significant, particularly in the heaviest patients. Charlson Comorbidity Index (CCI) was associated with FCDR (PR(CCI:3+ vs 0): 1.58; 95% CI: 1.19-2.11; p-trend = 0.009) and ARDI < 90% (p-trend < 0.001), as were individual comorbidities. Understanding dose reductions and their impact will be critical to optimizing care and improving survivorship.