Distribution of the Homologous Recombination-related (HRR) Genesmutationsand HRD in Breast Cancer

This is a cross-sectional and an observational study, investigator-initiated study in HER2-low breast cancer patients. Approximately 255 subjects with HRD (homologous recombination deficiency) assessment will be enrolled in this study to examine the distribution and features of HRD/HRR (homologous recombination repair). In this study, investigators plan to clarify the frequency of HRR/HRD in Chinese patients with HER2-low breast cancer. In addition, it is planned to investigate any association between invasive disease-free survival (iDFS)/overall survival (OS) and HRD/HRR in HER2-low breast cancer patients.

Inclusion Criteria: 1. Female patients aged 18-70 years with pathologically confirmed HER2-low breast cancer (defined as IHC 2+/ISH- or IHC 1+ per ASCO/CAP guidelines); 2. ECOG performance status of 0 or 1; 3. Treatment-naïve operable primary breast cancer with completed homologous recombination deficiency (HRD) assessment; 5）Absence of distant metastasis; 6）Availability of adequate tumor tissue and blood samples for biomarker analysis. Exclusion Criteria: 1. Recurrent or inoperable locally advanced breast cancer; 2. Bilateral breast cancer; 3. History of other malignant tumors within the past 5 years; 4. Incomplete clinical or pathological data.