Omission of axillary lymph node dissection in patients with breast cancer with axillary pathological complete response confirmed by stained region lymph node biopsy after neoadjuvant systemic therapy (SrLNB study): study protocol for a single-arm, single-centre, phase-II trial.

Introduction: Given that axillary lymph node dissection (ALND) may not contribute to local control or survival and could lead to increased arm morbidity, axillary de-escalation procedures have replaced ALND in patients achieving axillary pathologic complete response (apCR) after neoadjuvant systemic therapy (NST). However, the application of targeted lymph node biopsy, one of the de-escalation procedures, remains limited due to a lack of long-term follow-up studies.

Methods and analysis: This prospective, single-arm, open-label, non-inferiority, single-centre phase II trial targets breast cancer patients initially diagnosed with axillary metastasis who achieved apCR after NST. The study aims to validate the oncological safety of stained region lymph node biopsy (SrLNB) procedure. SrLNB is a novel de-escalation axillary surgery, which was developed and tested in our preliminary study. The primary endpoint of this trial is the 3-year invasive disease-free survival (iDFS). Secondary endpoints include local-regional recurrence, incidence of breast cancer-related lymphoedema and patient-reported outcomes. The 3-year iDFS in patients undergoing ALND is expected to be approximately 90%, with a non-inferiority margin of 10%, a significance level of 0.05, power of 0.8 and a loss-to-follow-up rate of 10%. The planned enrolment is 92 patients. The trial was initiated on 11 September 2023, with the first patient enrolled on 25 September 2023, and is scheduled to end in 2026.

Ethics and dissemination: The trial protocol received approval from the Human Research Ethics Committee of The First Affiliated Hospital with Nanjing Medical University in May 2023 (No. 2023-SR-169). All participants will provide informed consent. The study results will be disseminated through international peer-reviewed scientific journals, presentations at international scientific conferences and public lectures.

Trial registration number: NCT05939830.