This study aimed to compare survival outcomes of neoadjuvant (NAC) and adjuvant chemotherapy (AdC) within each breast cancer subtype and stage among older women.
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.
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.
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.

© 2023. The Author(s), under exclusive licence to The Japanese Breast Cancer Society.