Risk of Surgical Overtreatment in cN1 Breast Cancer Patients who Become ypN0 After Neoadjuvant Chemotherapy: SLNB Versus TAD.

Background: Two surgical approaches have emerged for axillary staging in cN1 breast cancer patients after neoadjuvant chemotherapy (NAC): sentinel lymph node biopsy (SLNB) and targeted axillary dissection (TAD). Direct comparisons of technical and oncological outcomes with SLNB versus TAD are lacking.

Methods: We routinely performed SLNB from 2017 to 2018 for cN1 breast cancer patients who converted to cN0 after NAC, then adopted TAD from 2019 to 2022. To minimize the false-negative rate (FNR), we required retrieval of ≥3 sentinel lymph nodes (SLN) (2017-2018) or retrieval of the clipped node (CN) and ≥2 SLN (2019-2022). In ypN0 cases meeting these criteria, axillary lymph node dissection (ALND) was omitted. We compared the rate of per-protocol required ALND due to technical failure of SLNB versus TAD and reported axillary recurrence rates.

Results: Among 191 cN1 ypN0 patients, 77 underwent SLNB and 114 underwent TAD. The overall rate of required ALND due to technical failure was 14.7% and did not differ between SLNB versus TAD (16.9% vs. 13.2%, p = 0.38). The most common technical failure with SLNB was retrieving <3 SLN (10.4%); for TAD, it was not retrieving the CN (7.1%). Median follow-up was 3.9 years for SLNB patients and 1.7 years for TAD patients; there were 1 (1.3%) and 0 (0.0%) axillary recurrences, respectively.

Conclusions: Sentinel lymph node biopsy and TAD for cN1 patients after NAC showed equivalent technical failure rates and low axillary recurrence rates. When applying strict criteria to minimize FNR of axillary staging surgery, approximately 15% of ypN0 patients may be overtreated with ALND.