Abstract ES7-2: Practical approach to the axilla after neoadjuvant chemotherapy: What the clinical trials don't address
Authors: Barrio A 
Published: May 2019

Abstract
Neoadjuvant chemotherapy (NAC) was initially used in patients with inoperable breast cancer to improve resectability, but it is also beneficial in women with operable breast cancer, particularly with respect to the axilla. Nodal pathologic complete response (pCR) rates among clinically node-positive patients treated with modern systemic therapy range from 35-49%. The ability to downstage the axilla and potentially avoid axillary lymph node dissection (ALND) is one of the greatest surgical advantages of NAC.
The optimal approach to the axilla after NAC varies based on the clinical nodal stage prior to NAC. In clinically node-negative patients, the use of sentinel lymph node biopsy (SLNB) after NAC has been well studied, with high identification rates and false-negative rates that are similar to the upfront surgery setting. In addition, regional recurrence rates are no different between clinically node-negative patients treated with SLNB alone after NAC, or those treated with upfront SLNB.
In clinically node-positive patients, 3 single-arm prospective trials have demonstrated that SLNB after NAC results in a false-negative rate &lt;10%, provided that the SLN technique is optimized with the use of dual mapping and retrieval of ≥3 negative SLNs. However, not all clinically node-positive patients are candidates for downstaging to SLNB with NAC. The prospective trials primarily enrolled patients with cT1-3N1 disease, and therefore study results should not be extrapolated to those patients presenting with cT4 and/or cN2/N3 disease, where ALND remains the standard of care. A more complicated issue is whether all clinically node-positive patients should even be considered for NAC, as the response rates in the nodes vary based on tumor subtype. Patients with hormone receptor (HR) positive/HER2 negative cancers have the lowest rates of nodal pCR compared to HER2 positive and triple-negative breast cancers. Specifically, patients with invasive lobular cancers have a low probability of nodal pCR with NAC, raising the question as to whether NAC should even be considered in these patients due to limited surgical downstaging.
As all patients in the prospective trials had an ALND, the frequency with which ALND could be avoided with the use of NAC in clinically node-positive patients was not addressed, although more recent data have demonstrated that approximately 50% will achieve a nodal pCR and avoid ALND. Indications for ALND after NAC include any positive SLN (including micrometastases and isolated tumor cells), failed mapping, or patients presenting with inoperable breast cancer. Nodal recurrence rates among clinically node-positive patients treated with SLNB alone after NAC are largely unknown, with only one small study demonstrating low regional recurrence rates.
Ultimately, the optimal treatment strategy to avoid ALND in patients with operable breast cancer is complex and based on a combination of tumor subtype, clinical nodal status, and type of breast surgery performed. With the continued use of modern systemic therapy and improved radiation techniques for breast cancer, our ability to de-escalate surgical care and reduce the morbidity of surgery, while still maintaining excellent disease control, has become our new standard of care.
Citation Format: Barrio A. Practical approach to the axilla after neoadjuvant chemotherapy: What the clinical trials don't address [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr ES7-2.