Incidence of Lymph Node Involvement in Clinically Node-Negative Breast Cancer Following Neoadjuvant Chemotherapy: Rationale for Selective Omission of Sentinel Lymph Node Biopsy.

Purpose: Neoadjuvant chemotherapy (NAC) is now frequently utilized for earlier stage breast cancer. Historically, removing axillary lymph nodes (LN) has guided treatment decisions and reduced regional recurrence, yet its utility in clinically node-negative (cN0) patients following NAC has yet to be elucidated. This study evaluated the incidence of residual occult pathologic nodal disease after NAC in cN0 breast cancer and associated clinicopathologic risk factors.

Methods: A retrospective study of 249 cN0 patients who received NAC at our institution from 2010-2021 was performed. Clinical and pathologic tumor features were compared between 2 groups: persistent LN- versus LN+ after NAC.

Results: The study group comprised 166 patients: 19 (11.4%) had pathologic LNs positive following NAC. Patients with LN+ (n = 19) versus LN- (n = 147) had greater mean clinical tumor size (P < .01), higher clinical T stage (P < .001), invasive lobular cancer (P < .01), lymphovascular invasion (P 0.01), and ER+ HER2- phenotype (P < .01). Conversely, LN- patients more likely had HER2+ tumors (P < .01) and in-breast pathologic complete response (P < .05). Sentinel LN biopsy (SLNB) obtained a mean of 3.8 LNs with 2 (1.2%) patients having ≥ypN2. At 46 months median follow-up, 1 (0.6%) axillary recurrence occurred.

Conclusions: There is a low incidence of both residual occult disease in the axilla and axillary recurrence in cN0 breast cancer patients following NAC. Many of these patients may avoid axillary surgery, or at a maximum, undergo SLNB alone with low concern for axillary recurrence.