What Would it be Like if the Results of the SOUND Trial Were Applied in Portugal?- A Speculative Analysis Based on Real-World Data

Introduction Sentinel lymph node biopsy (SLNB) is the standard for axillary staging in breast cancer (BC). The prevalence of nodal metastases is ∼30–40% and correlates with tumor size. For T1 tumors, nodal positivity is ∼20%, with 70% of these being micrometastases. The SOUND study demonstrated that omitting SLNB is not inferior to performing it in small tumors with negative axillary ultrasound. The objectives of this study were to evaluate the diagnostic capability of preoperative axillary ultrasound and to estimate the impact of applying SOUND criteria on staging and adjuvant treatment planning. Materials and Methods We conducted a retrospective analysis of 597 consecutive patients with invasive BC c/uT1 c/uN0, diagnosed and treated between 2015 and 2020. Sentinel lymph nodes were assessed using the OSNA technique. Results Demographic and treatment data were comparable to the SOUND population. Sentinel node metastases were found in 24.1% of cases (including pN0sn i+ and pN1sn mic), higher than the 17.3% in SOUND. However, considering only pN1sn and pN2sn, metastases were 9.5%, closely resembling SOUND's 8.7%. Preoperative axillary ultrasound showed high specificity (97.7%) but very low sensitivity (7.0%) for detecting macrometastases. MRI had the highest sensitivity (31.8%). Biological features, staging, treatments and survival were overall consistent with the SOUND trial. Applying SOUND criteria would mean 10.2% of patients losing staging, which could impact chemotherapy and CDK inhibitor eligibility. Conclusion Despite methodological differences in sentinel node evaluation, the SOUND results may be applicable to our population. Additional imaging adds little value beyond axillary physical assessment in this context. Micro Abstract This study assessed the diagnostic performance of preoperative axillary ultrasound and the clinical impact of applying SOUND trial criteria in T1 invasive breast cancer. Among 597 c/uT1 c/uN0 patients, sentinel node metastases occurred in 24.1%, but only 9.5% were macrometastases, closely resembling SOUND data. Axillary ultrasound showed high specificity (97.7%) but poor sensitivity (7.0%) for macrometastatic disease. Applying SOUND criteria would omit axillary staging in 10.2% of patients, potentially influencing systemic therapy decisions. These findings appear to support that extrapolation of SOUND criteria to this population may be safe, with minimal added benefit from advanced axillary imaging in routine practice.