Axillary lymph node yield following axillary dissection in biopsy-proven node-positive breast cancer: neoadjuvant systemic therapy versus primary surgery

Background: Neoadjuvant systemic therapy (NAST) induces morphological changes within the axilla; however, its impact on lymph node yield (LNY) following axillary lymph node dissection (ALND) is less clear. Methods: A retrospective cohort study was performed including female patients who underwent ALND for biopsy-proven node-positive breast cancer within Western Sydney Local Health District hospitals between 2010 and 2022. Patients were grouped by receipt of NAST versus primary surgery (PS). LNY was compared between groups. Within the NAST group, univariate and multivariable logistic regression analyses identified variables associated with LNY ≥ 10. Results: Among 768 patients, 217 (28.3%) received NAST and 551 (71.7%) underwent PS. Median LNY was lower following NAST compared to PS (17 [IQR: 10] vs. 21 [IQR: 10], p < 0.001), with fewer NAST patients achieving a LNY ≥ 10 compared to PS (90.8% vs. 97.5%, p < 0.001). On multivariable analysis, lymphovascular invasion (LVI) was associated with reduced odds of achieving a LNY ≥ 10 (OR: 0.26, 95% CI: 0.09–0.80, p = 0.019), whereas the HR+/HER2− subtype was associated with increased odds (OR: 3.89, 95% CI: 1.20–12.7, p = 0.024). Neither complete pathological response nor treatment effect was associated with reduced LNY. Conclusion: NAST was associated with a modest but statistically significantly lower LNY, although median yields exceeded traditional thresholds and lymph node ratio was preserved. Following NAST, LNY appears influenced by tumour biology rather than surgical adequacy. These findings reinforce the need to interpret historic numeric thresholds cautiously, with greater emphasis on residual disease and surgical intent in modern practice.