Durable carbon tattooing reveals target–sentinel discordance in low-volume residual axillary disease after neoadjuvant chemotherapy

Accurate axillary staging after neoadjuvant chemotherapy (NAC) requires assessment of the lymph node proven metastatic before treatment. This target node may not correspond to the sentinel node identified after NAC, particularly when residual nodal disease is limited to micrometastases or isolated tumor cells (ITCs). Carbon tattooing may provide durable identification of the pre-treatment metastatic node. We evaluated carbon persistence in clip-verified target nodes and examined target–blue dye concordance according to residual nodal burden. This prospective two-center study included 83 patients with biopsy-proven cT1–3N1M0 breast cancer. Before NAC, suspicious axillary nodes underwent ultrasound-guided core needle biopsy. After pathological confirmation, one to three metastatic target nodes were marked with carbon suspension and metallic clips. At surgery, clipped target nodes were wire-localized, and sentinel mapping was performed with blue dye alone. The primary outcome was intraoperative visualization of carbon in clip-verified target nodes. Secondary outcomes were target–blue dye concordance and localization of residual macrometastasis (MacroM), micrometastasis (MicroM), and ITCs. Carbon remained visually identifiable in all retrieved clip-verified target nodes after NAC. Blue dye identified lymph nodes during SLNB in 62/83 patients (74.7%); stained nodes were identified only during subsequent ALND in 7/83 (8.4%), and no blue-dye–stained node was identified in 14/83 (16.9%). Overall target–blue dye concordance was 56.6%. Target-node–only residual disease was found in 15/42 patients with MacroM (35.7%), 12/30 with MicroM (40.0%), and 27/41 with ITCs (65.9%). Within this blue-dye single-tracer protocol, no residual disease component was identified exclusively in blue-dye–mapped nodes. These findings describe target–blue dye discordance within a single-tracer protocol and should not be interpreted as a comparison with contemporary dual-tracer SLNB. Carbon tattooing remained durable throughout NAC and supported reliable retrieval of biopsy-proven metastatic target nodes. Target–blue dye discordance was most evident for low-volume residual disease. These findings support direct target-node retrieval alongside sentinel mapping, without implying superiority over contemporary dual-tracer SLNB or inadequacy of optimized sentinel-node mapping.