Comparing survival outcomes between neoadjuvant and adjuvant chemotherapy within breast cancer subtypes and stages among older women: a SEER-Medicare analysis

Background This study aimed to compare survival outcomes of neoadjuvant (NAC) and adjuvant chemotherapy (AdC) within each breast cancer subtype and stage among older women. Methods Older (≥ 66 years) women newly diagnosed with stage I–III invasive ductal breast cancer during 2010–2017 and treated with both chemotherapy and surgery within one year were identified from the Surveillance, Epidemiology, and End Results (SEER)-Medicare database. Analyses were performed within each of six groups, jointly defined based on subtype (hormone receptor [HR]-positive/human epidermal growth factor receptor 2 [HER2]-negative, HER2 + , and triple-negative) and stage (I–II and III). Kaplan–Meier curves and multivariable Cox models were used to compare overall and recurrence-free survival between NAC and AdC, with optimal full matching performed for confounding adjustment. Results Among 8,495 included patients, 8,329 (20.6% received NAC) remained after matching. Before multiple testing adjustment, Cox models showed that NAC was associated with a lower hazard for death among stage III HER2 + patients (hazard ratio = 0.347, 95% confidence interval CI 0.161–0.745) but a higher hazard for death among triple-negative patients (stage I–II: hazard ratio = 1.558, 95% CI 1.024–2.370; stage III: hazard ratio = 2.453; 95% CI 1.254–4.797). A higher hazard for death/recurrence was associated with NAC among stage I–II HR + /HER2– patients (hazard ratio = 1.305, 95% CI 1.007–1.693). No significant difference remained after multiple testing adjustment. Conclusions The opposite trends (before multiple testing adjustment) of survival comparisons for advanced HER2 + and triple-negative disease warrant further research. Caution is needed due to study limitations such as cancer stage validity.