Axillary Management After Neoadjuvant Endocrine Therapy for Hormone Receptor-Positive Breast Cancer.

Background: Data to guide axillary management after neoadjuvant endocrine therapy (NET) remain limited.

Methods: We analyzed type of axillary surgery [sentinel lymph node biopsy (SLNB) vs. axillary lymph node dissection (ALND)] and residual nodal disease burden after NET in two cohorts of patients with cT1-4N0-1M0 hormone receptor-positive/human epidermal growth factor receptor 2-negative (HR+/HER2-) breast cancer: Dana-Farber/Brigham and Women's Cancer Center (DFBWCC) cohort (2015-2018) and the National Cancer Data Base (NCDB) cohort (2012-2016). Cox proportional hazard regression was used to determine adjusted 5-year overall survival (OS) by type of axillary surgery.

Results: Ninety-four (4.3%) of 2191 HR+/HER2- DFBWCC patients and 4363 (1.5%) of 283,344 NCDB patients were selected for NET. Of those who underwent axillary surgery, 30 (43.5%) in the DFBWCC cohort and 1583 (40.6%) in the NCDB cohort had ALND. Over 90% of cN0 patients in both cohorts had fewer than three positive nodes on final pathology [44 (95.7%) DFBWCC and 2945 (91.3%) NCDB]. In contrast, only 7 (30.4%) DFBWCC patients and 342 (50.7%) NCDB cN1 patients had fewer than three positive nodes. In the DFBWCC patients, there were no locoregional recurrences and four distant recurrences. In the NCDB, 5-year OS did not differ by type of axillary surgery regardless of residual nodal disease burden: 96.6% SLNB versus 97.9% ALND for 0 positive nodes; 84.4% versus 84.4% for one to two positive nodes, and 75.9% versus 77.3% for three or more positive nodes (all p > 0.10).

Conclusions: In cN0 patients selected for NET, > 90% have fewer than three positive nodes at surgery. The lack of a survival difference between SLNB and ALND suggests an opportunity to de-escalate treatment of the axilla in patients with limited residual nodal disease.