Locoregional recurrence after neoadjuvant versus adjuvant chemotherapy based on tumor subtypes in patients with early-stage breast cancer: A multi-institutional retrospective cohort study.

Background: Neoadjuvant chemotherapy (NACT) for early-stage breast cancer is associated with an increased risk of locoregional recurrence (LRR). We investigated whether the risk of LRR after NACT varies across tumor subtypes.

Methods: We retrospectively reviewed the medical records of women who underwent breast-conserving surgery for breast cancer at three institutions between January 1, 2004, and December 31, 2018. Patients received either NACT or adjuvant chemotherapy (ACT), followed by radiotherapy. LRR was analyzed according to the hormone receptor (HR) and human epidermal growth factor receptor-2 (HER2) status using propensity score matching, log-rank test, and Cox regression analysis.

Results: Among 10,328 patients, 2479 (24.0 %) received NACT. Within the median follow-up of 84.5 (IQR, 35.1-118.5) months, the 10-year LRR-free survival rates were 94.5 % and 90.7 % for the ACT and NACT groups, respectively (hazard ratio: 2.04, 95 % confidence interval [CI]: 1.68-2.46, p < 0.0001). NACT was significantly associated with higher LRR in the HR+/HER2- (hazard ratio: 2.52, 95 % CI: 1.83-3.46, p < 0.0001) and HR-/HER2- (hazard ratio: 1.85, 95 % CI: 1.37-2.50, p < 0.0001) subtypes. In the HR+/HER2- subtype, the elevated risk remained significant after propensity-score matching and Cox-regression analysis. However, NACT was not associated with LRR in the HR-/HER2- subtype after adjusting for other variables. Annual LRR pattern among the HR+/HER2- subtype showed the highest incidence in the early period of treatment.

Conclusion: Patients with the HR+/HER2- subtype showed an increased risk of LRR after NACT, while those with other subtypes showed comparable LRR-free survival.