Association between adjuvant chemotherapy and outcomes in resected locoregional recurrence of hormone receptor-positive HER2-negative breast cancer: a multi-institutional retrospective study

Background: To evaluate the association of adjuvant chemotherapy and prognosis for locoregional recurrence (LRR) in hormone receptor (HR)-positive human epidermal growth factor receptor 2 (HER2)-negative subtype breast cancer.
Patients and methods: We carried out a multi-institutional retrospective cohort study in patients with breast cancer who developed HR-positive HER2-negative LRR. Patients who underwent curative surgery for LRR between 2014 and 2018 were categorized based on whether they received adjuvant chemotherapy for LRR (CTx versus no-CTx). Invasive disease-free survival (iDFS) was evaluated between the groups by Cox proportional hazards analysis. The primary analysis used a double-robust Cox model incorporating inverse probability of treatment weighting, and a sensitivity analysis using propensity score matching was also carried out.
Results: A total of 958 patients were included. The median time from the primary surgery to LRR diagnosis was 9.5 years (interquartile range 3.1-10.1 years). There were 235 patients (25%) in the CTx group and 722 (75%) in the no-CTx group. Among all patients, the 5-year iDFS rate was 75.4% [95% confidence interval (CI) 72.4% to 78.2%]. Multivariate analysis showed better iDFS in the CTx group (hazard ratio 0.70, 95% CI 0.49-0.99, P = 0.045). Sensitivity analysis supported these findings. Subgroup analyses showed that the CTx group had better iDFS in cases with non-ipsilateral breast tumor recurrence (IBTR), recurrences during adjuvant endocrine therapy for primary breast cancer, and without perioperative chemotherapy for primary breast cancer. Secondary analysis showed no significant difference with a worse trend toward overall survival in the CTx group with multivariate Cox proportional hazards analysis.
Conclusion: Adjuvant chemotherapy for HR-positive HER2-negative LRR was associated with better iDFS, particularly in cases of non-IBTR, recurrences during adjuvant endocrine therapy, and no prior perioperative chemotherapy for their primary tumor. However, the retrospective design and inability to distinguish true recurrences from new primary tumors in IBTR warrant cautious interpretation.