Mattea Reinisch, Efstathia Cremer, Kilian Pankert, Diana Weber, Volker Hanf, Katja Engellandt, Sebastian Hentsch, Cordula Müller, Peter Dall, Matthias Losch, Petra Deuschle, Alexander Traut, Satyen Shenoy, Anita Engel, Dorothea Schindowski, Sherko Kuemmel, Simona Gipe
Background: Neoadjuvant systemic therapy (NST) enables tumor downsizing and increases the feasibility of breast-conserving surgery (BCS) in patients with early breast cancer (EBC). Reliable tumor localization after NST remains challenging, particularly in patients with a complete clinical response. If clips are not visible on ultrasound, stereotactic mammography-guided wire localization is required, which involves additional radiation exposure and may increase patient discomfort and procedural complexity. The 3D-shaped Tumark® Vision clip may enable ultrasound-guided localization after NST. Methods: In this prospective multicenter registry study (NCT04468113), 324 patients with biopsy-proven EBC scheduled for NST and breast-conserving surgery were enrolled across 19 German centers. Clip placement was performed under ultrasound guidance prior to NST, and clip detectability was assessed at predefined time points during therapy (4-8, 9-12, and ≥13 weeks after treatment initiation). Detection rates, visualization, and preoperative localization methods were recorded. Non-detectable clips required stereotactic wire localization, whereas ultrasound-guided localization was performed for detectable clips. Results: The preoperative detection rate was 91.1%. Clip detectability was higher in patients with longer NST durations and partial response by imaging. Ultrasound-guided wire localization was feasible in 214 patients (83.9%); among these, 165 patients (64.7%) underwent localization without and 49 patients (19.2%) with post-procedural mammographic verification. Stereotactic localization was required in 41 patients (16.1%), primarily due to non-visualization of the clip on ultrasound. The accuracy of ultrasound for residual tumor assessment was moderate (72.0%), with a sensitivity of 70.7%, indicating limitations in its ability to reliably assess residual tumor extent as a standalone modality. Conclusions: The 3D nickel-titanium clip enables ultrasound-guided tumor localization after NST in the majority of patients with early breast cancer, although additional mammographic guidance remains necessary in a relevant proportion of cases.