Previous studies suggest that among patients receiving trastuzumab monotherapy, a HER2/CEP17 ratio >7.0 (ultra-high expression) is associated with poorer disease-free survival (DFS). Dual-target therapy (trastuzumab + pertuzumab) has become the standard treatment for high-risk HER2-positive breast cancer; however, whether it can predict outcomes in patients with ultra-high HER2 expression remains unsupported by clinical data. To analyze the clinicopathological characteristics and prognostic relationship between the HER2 ultra-high expression group and the normal expression group in non-metastatic HER2-positive breast cancer patients who received dual-target therapy.

Inclusion Criteria:

1. Age ≥18 years.
2. Pathologically confirmed primary breast cancer, clinical stage I-III (AJCC 8th Edition).
3. HER2-positive status confirmed by FISH testing (per ASCO/CAP guidelines) with available HER2/CEP17 ratio.
4. Received at least one dose of dual-target therapy (trastuzumab combined with pertuzumab) in the adjuvant or neoadjuvant setting.
5. Underwent curative-intent surgery (mastectomy or breast-conserving surgery).

Exclusion Criteria:

1. Presence of distant metastasis (Stage IV) or contralateral breast cancer at initial diagnosis.
2. Previous anti-HER2 targeted therapy prior to dual-target treatment.
3. Missing key clinical data (e.g., HER2 FISH results, treatment regimen, surgery date).
4. Carcinoma in situ or occult breast cancer, non-primary breast cancer, or concurrent other malignancies.
5. Loss to follow-up or follow-up duration <3 months (unless recurrence or death occurred within this period).

HER2-positive patients with breast cancer were enrolled between January 2020 and December 2023.