Associated factors and outcomes of delaying adjuvant chemotherapy in breast cancer by biologic subtypes: a National Cancer Database study

Purpose Several studies have evaluated the role of delayed initiation of adjuvant chemotherapy (AC) in breast cancer (BC), but the results have remained controversial and an optimal time has not been defined. Our aim was to determine the effect of time to starting AC from the date of surgery on survival of BC patients, based on estrogen receptor (ER), progesterone receptor (PR) and human epidermal growth factor receptor 2 (HER2) status, using data from the National Cancer Database (NCDB). Methods A total of 332,927 Stage I-III BC patients who received AC from 2010 to 2016 were analyzed. We included all ER, PR and HER2 statuses and excluded patients with stage 4 and stage 0 (DCIS) disease. The cohort was divided into five groups based on the time of initiating AC from the date of the most definitive surgery i.e., <= 30 days, 31-60 days, 61-90 days, 91-120 days and > 120 days. They were further divided into five subgroups based on the receptor status. Results Hazard ratio (HR) estimates and Kaplan-Meier (KM) analysis shows that starting AC by 31-60 days shows the best survival outcome in all the subtypes, except in hormone positive/HER2 negative BC in which 31-60 days and 61-90 days have similar outcomes. Conclusions After surgery for BC, it takes around 4-6 weeks to begin AC and delay in initiating the same leads to poor outcomes. Our results are particularly significant in triple-negative breast cancer (TNBC), similar to prior studies showing a benefit to starting AC as early as possible after surgery.