Beyond Nodal Diagnosis: Preoperative Axillary Core Needle Biopsy for Predicting Axillary Tumor Burden in the Era of Axillary De‐Escalation

BACKGROUND AND OBJECTIVES: With ongoing axillary treatment de-escalation in breast cancer, preoperative assessment of axillary tumor burden has become increasingly important. We investigated whether pathological information from preoperative axillary lymph node (LN) core needle biopsy (CNB) could stratify final axillary tumor burden. METHODS: We included 473 patients who underwent ultrasound-guided CNB of suspicious axillary LNs. Associations of metastatic focus size and extranodal extension (ENE) on CNB with final axillary tumor burden were evaluated. RESULTS: Of 473 patients, 212 had positive and 261 had negative CNB findings. Among 135 CNB-positive patients undergoing upfront surgery, CNB metastatic focus size correlated with the maximum metastatic focus size in resected LNs (ρ = 0.72, p < 0.001) and the number of positive LNs (ρ = 0.269, p = 0.0016). All 21 patients with a CNB metastatic focus ≤ 2 mm had two or fewer positive LNs. ENE independently predicted pN2-3 disease (OR, 3.61; 95% CI, 1.51-8.68; p = 0.004). Among patients receiving primary systemic therapy, CNB metastatic focus size did not independently predict total pathological complete response. None of 244 CNB-negative patients undergoing upfront surgery had pN2 or higher disease. CONCLUSIONS: Pathological information from preoperative axillary LN CNB may help stratify axillary tumor burden and support individualized axillary risk assessment in the era of treatment de-escalation.