Can we avoid axillary lymph node dissection in N2 breast cancer patients with chemo-sensitive tumours such as HER2 and TNBC?

Purpose: To find a group of cN2 patients or patients with high axillary burden who become ypN0 after neoadjuvant chemotherapy (NACT) and who may benefit from avoiding a lymphadenectomy.
Methods: A retrospective observational cohort study was conducted with 221 clinically staged N2 patients or patients with at least 3 suspicious lymph nodes found by ultrasound at diagnosis. The predictive factors for ypN0 analysed were age, MRI-determined tumour size, histological subtype, the Nottingham histologic grade, surrogate molecular subtype, ki-67 and vascular invasion when present. Clinical and radiological responses after NACT were also evaluated. Univariate and multivariate analyses by logistic regression were performed. Distant disease-free survival (DDFS) was calculated in relation to the status of the axillary lymph nodes after NACT.
Results: After NACT, 89 patients (40.3%) had axillary pathologic complete response (pCR) (ypN0) and 132 (59.7%) had residual axillary disease (ypN+). Molecular surrogate subtype, Ki-67 expression, and the clinical and radiological responses to NACT were the only independent factors associated with ypN0. Axillary pCR was observed more often in HER2-positive and triple-negative tumours than in luminal ones (OR 7.5 and 3.6, respectively). DDFS was 88.7% (95% CI 80.7-96.7%) for ypN0 and 56.2% (95% CI 32.1-80.3%) for ypN+ (p = 0.09).
Conclusions: In HER2-positive and triple-negative breast cancer patients staged as cN2 or with high axillary burden before NACT, a sentinel lymph node biopsy after NACT could be recommended if there is a clinical and radiological response.