Contemporary Trends in Axillary Surgery for ER-Positive, HER2-Negative Breast Cancer Stratified by Neoadjuvant Endocrine Therapy, Neoadjuvant Chemotherapy, or Upfront Surgery

Background De-escalation of axillary surgery for hormone receptor-positive breast cancer has gained traction, but guidelines for axillary management after neoadjuvant endocrine therapy (NET) remain ill-defined. Methods Female patients age ≥50 years with clinical T1-4c, N0-1, ER+/HER2–<PUB4> breast cancer (2012–2021) were selected from the National Cancer Database (NCDB) and divided into three groups based on treatment: upfront surgery, neoadjuvant chemotherapy (NAC), or NET. Axillary surgery was categorized as no axillary surgery, sentinel lymph node biopsy (SLNB) alone, sentinel lymph node biopsy followed by axillary lymph node dissection (ALND), or ALND alone. Descriptive analysis and logistic regression were used to identify factors associated with ALND, and survival analysis was performed. Results The inclusion criteria were met by 792,581 patients. The majority underwent surgery first (94.3 %), whereas 2.6 % received NAC and 3.1 % received NET. After adjustment, the odds of undergoing ALND were shown to be higher for those receiving NAC (odds ratio [OR], 1.18; 95 % confidence interval [CI], 1.12–1.24) or NET (OR, 1.10; 95 % CI, 1.05–1.14) than for those receiving surgery first ( p < 0.001). The patients receiving NET were less likely to convert from cN+ to ypN0 (8.3 % vs NAC 19.6 %; p < 0.001), but they still were less likely to undergo ALND after SLNB. Overall survival was highest among the patients in the surgery-first group regardless of clinical nodal status ( p < 0.001). Conclusions Although the patients receiving NET had lower rates of nodal pathologic complete response, this did not translate to higher conversion to ALND after SLNB, suggesting that providers do not interpret residual nodal disease after NET the same way as after NAC.