Neratinib is an oral, irreversible pan-HER tyrosine kinase inhibitor. Current treatment guidelines recommend neratinib as an extended adjuvant therapy for HER2-positive breast cancer patients to further reduce the risk of recurrence.

Even when HER2-positive breast cancer patients achieve pathological complete response (pCR) after neoadjuvant therapy, those with high-risk factors (such as large tumors [cT3/T4] or lymph node-positive disease) still face a risk of cancer returning. However, there is limited data on the effectiveness and safety of neratinib in these patients.

This study aims to provide real-world evidence on how well neratinib works in high-risk HER2-positive breast cancer patients who achieved pCR, helping to improve treatment strategies for Chinese patients.

This study is a single-arm prospective study with historical controls as external comparators

Inclusion Criteria:

1. Age ≥18 years, female
2. Clinical stage ≥cT3 or ≥cN1, regardless of hormone receptor (HR) status
3. HER2-positive: HER2 IHC 3+ or IHC 2+ with ISH+
4. Achieved pathological complete response (pCR) after neoadjuvant therapy
5. Completed 1 year of standard adjuvant therapy (including trastuzumab), with ≤6 months between the last adjuvant treatment and starting neratinib
6. No evidence of recurrence or metastatic disease (confirmed by clinical/imaging exams after completing standard adjuvant therapy and before starting neratinib)
7. Left ventricular ejection fraction (LVEF) ≥50%
8. ECOG performance status 0-1

Exclusion Criteria:

1. Hypersensitivity to any component of the investigational drug
2. Inability to swallow oral medication
3. Participation in another interventional clinical trial within 4 weeks before enrollment, or planned participation during this study
4. Use of any investigational drug within 14 days prior to treatment initiation
5. Concurrent chemotherapy, radiotherapy, immunotherapy, or biologic therapy for breast cancer
6. Severe psychiatric disorders preventing compliance with informed consent, treatment, or follow-up procedures
7. Pregnancy, lactation, or plans for pregnancy in the near future
8. Other significant medical conditions or laboratory abnormalities that, in the investigator's judgment, make participation unsuitable

This study focuses on HER2-positive early breast cancer (EBC) patients who achieved pathological complete response (pCR) following neoadjuvant therapy but present with high-risk features (such as initial clinical stage cT3/T4 tumors or node-positive disease). These patients must have completed standard adjuvant therapy (including trastuzumab-based regimens) and initiated neratinib as extended adjuvant treatment within 6 months after completing their standard therapy.