Breast cancer metastasis burden in sentinel nodes analysed using one-step nucleic acid amplification predicts axillary nodal status

•NSLN metastasis risk in breast cancer patients undergoing SLNB analysis using OSNA.•Categorising by extent of sentinel node positivity predicts NSLN metastasis risk.•A multiple incomplete positive SLNB of micrometastases has low NSLN metastasis risk.•SLNB metastasis size better predicts NSLN involvement than total CK-19 mRNA count.

BackgroundIn breast cancer patients undergoing sentinel lymph node biopsy (SLNB) analysis using one-step nucleic acid amplification (OSNA), clarity is required as to the risk factors for non-sentinel lymph node (NSLN) involvement upon axillary lymph node dissection (ALND). This study aims to identify these factors, including categorising by extent of sentinel node positivity: solitary positive node (solitary), multiple nodes with some positive (multiple incomplete positive), or multiple nodes all of which are positive (multiple all positive).MethodsWe conducted a cohort study using prospectively collected data on 856 SLNBs analysed using OSNA, from patients with cT1-3 clinically node-negative invasive breast cancer. ALND was performed for 289 positive SLNBs.ResultsNSLN metastases were identified in 73 (25.3%) ALNDs. Significant factors for NSLN involvement on multivariate analysis were: SLNB macrometastases (cytokeratin-19 mRNA count >5000 copies/μl) (adj.OR = 3.01; 95% CI, 1.61-5.66; p = 0.0006), multiple all positive vs. multiple incomplete positive SLNB (adj.OR = 2.92; 95% CI, 1.38-6.19; p = 0.0050), and undergoing mastectomy (adj.OR = 1.89; 95% CI, 1.00-3.55; p = 0.0486). Amongst multiple incomplete positive SLNBs, an 8.8% NSLN risk was identified when only micrometastases were present.ConclusionExtent of sentinel lymph node positivity measured using OSNA predicts NSLN metastasis risk, aiding decisions surrounding axillary treatment.