Abstract
<title>Abstract</title> <p>Background The impact of treatment delay on breast cancer survival across disease stages remains inconsistent across studies. We evaluated the association between time to treatment initiation (TTI) and overall survival by disease stage among Korean women with breast cancer. Methods A retrospective cohort study was conducted using the Breast Cancer Collaborative Stage-Linked Database (2012–2019), which was established under the Korean Clinical Data Utilization for Research Excellence (K-CURE) project. TTI was categorized as ≤ 30 days (reference), 31–60 days, ≥ 61 days, or no treatment within 1 year. Stage-stratified Cox proportional hazards models were used to estimate adjusted hazard ratios (aHRs) for overall survival. Subgroup analyses were performed according to molecular subtype and comorbidity status. Results A total of 16,495 women were included. Among treated patients, TTI was not significantly associated with overall survival in patients with stage I, II, or IV disease. In patients with stage III disease, a delay of ≥ 61 days was associated with a 50% higher risk of death (aHR, 1.50; 95% CI, 1.04–2.16). In the overall cohort, this delay was associated with worse survival among patients with triple-negative breast cancer (aHR, 1.75; 95% CI, 1.10–2.78) and HR+/HER2 + tumors (aHR, 1.41; 95% CI, 1.04–1.92). Among patients with stage III disease, the association was especially pronounced for those with preexisting cardiovascular disease (aHR, 5.28; 95% CI, 1.78–15.68). Conclusions Among Korean women with stage III disease, a treatment delay of ≥ 61 days was associated with worse overall survival. The association was more pronounced in aggressive subtypes and in those with preexisting cardiovascular disease, highlighting the need to minimize avoidable delays in these high-risk groups.</p>