Understanding the association between body mass index and chemotherapy dose reductions in women treated for stage I-IIIA breast cancer

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.