Axillary Surgery After Neoadjuvant Chemotherapy for Breast Cancer: Population-Based Trends Over Time.

Background: Sentinel lymph node biopsy (SLNB) after neoadjuvant chemotherapy (NAC) is recommended for patients initially presenting with cN1 disease and evidence of clinical/imaging response after NAC. We aimed to describe real-world population changes in management.

Methods: We completed a population-based cohort study including adult women undergoing NAC followed by surgery for cT1-3N1 breast cancer between 1 April 2012 and 31 January 2020 in Ontario, Canada. Axillary surgeries (SLNB, axillary lymph node dissection [ALND], or SLNB followed by ALND) were studied over time using the Cochran-Armitage test, while multivariable logistic regression evaluated factors associated with surgery type.

Results: Overall, 2563 patients were analyzed (37.9% were HER2-positive [HER2+ve], 42.3% were hormone receptor-positive and HER2-ve [HR+/HER2-ve], and 19.8% were triple-negative [TN]). 593 (23.1%) patients underwent SLNB and 1860 (72.6%) underwent ALND, while 110 (4.3%) patients underwent SLNB + ALND. From 2012 to 2020, SLNB increased from 5.7 to 29.9% (p < 0.01) and SLNB + ALND increased from 1.7 to 4.7% (p < 0.01), while ALND decreased from 92.6 to 65.4% (p < 0.01). Similar trends were identified across all receptor groups. After adjustment, patients who underwent SLNB had fewer comorbidities (odds ratio [OR] 1.82, 95% confidence interval [CI] 1.03-3.19), smaller tumors (T2 vs. T3: OR 1.52, 95% CI 1.21-1.92; T1 vs. T3: OR 1.56, 95% CI 1.14-2.13), and had surgery later in the study period (OR 1.32, 95% CI 1.25-1.38).

Conclusions: In alignment with current practice guidelines, de-escalation of axillary surgery to SLNB has increased over time for patients after breast cancer NAC.