This multicenter, open-label, controlled phase III clinical trial aims to investigate the clinical value of iodine-125 radioactive seed markers in patients with early or locally advanced breast cancer undergoing neoadjuvant therapy. Current guidelines support pre-treatment marking of primary tumors and lymph nodes to improve surgical accuracy and reduce false-negative rates in sentinel lymph node biopsy after neoadjuvant therapy. However, the optimal marking method remains unclear. Iodine-125 seeds offer potential advantages, including high localization accuracy, improved identification of metastatic lymph nodes, and favorable cost-effectiveness compared with other wireless or metallic markers.
Eligible patients will be randomized 1:1 into either the experimental or control group.
Experimental group: Under ultrasound guidance, iodine-125 seeds (0.1-0.3 mCi) will be implanted into the primary breast tumor and biopsy-proven positive axillary lymph nodes before the first cycle of neoadjuvant therapy. Seed positions will be monitored throughout therapy by ultrasound, mammography, and MRI to confirm they have not migrated (defined as ≤5 mm deviation from baseline).
Control group: Patients will receive neoadjuvant therapy without seed implantation.
All participants will receive standard neoadjuvant systemic therapy according to disease subtype and investigator assessment. Following therapy, participants will undergo surgery, and pathological responses will be evaluated by predefined criteria. Patients will be followed for at least five years to assess invasive disease-free survival and other outcomes.
Objectives and Endpoints
The primary objective is to compare the pathological complete response (pCR) rate between the seed-marked arm and the control arm. pCR is defined as ypT0/is and ypN0, meaning no residual invasive carcinoma in the breast or regional lymph nodes.
Secondary objectives include breast pCR (bpCR), axillary pCR (apCR), and invasive disease-free survival (iDFS). An exploratory endpoint will evaluate whether iodine-125 seeds may stimulate immune activation by monitoring peripheral blood CD4+/CD8+ T-cell ratios during treatment.
Study Rationale
Neoadjuvant therapy plays a critical role in downstaging tumors and improving surgical options. Achieving pCR is associated with significantly improved long-term survival outcomes, particularly for HER2-positive and triple-negative breast cancer. Our preliminary work suggests that patients receiving iodine-125 seed implantation prior to neoadjuvant therapy show improved pCR rates across molecular subtypes compared with patients without seed placement. Therefore, this trial aims to confirm the effectiveness and safety of radioactive seed marking in a rigorously controlled phase III study and to explore its biological mechanisms.
Safety Monitoring
Adverse events and serious adverse events will be recorded from the time informed consent is obtained until postoperative follow-up. All safety assessments, including laboratory tests, imaging, and clinical examinations, will be performed according to protocol-defined schedules. The relationship between adverse events and seed implantation will be evaluated by investigators following prespecified criteria.
This trial is expected to provide high-quality evidence regarding the clinical utility of iodine-125 seeds in improving response assessment, enhancing pCR rates, and potentially affecting long-term prognosis in breast cancer patients receiving neoadjuvant therapy. It may also contribute novel insights into radiotherapy-related immunomodulatory mechanisms.
