Abstract: Background and purpose: Breast cancer is the most common malignancy in women worldwide, and its incidence continues to rise. Postoperative radiotherapy for breast cancer can effectively improve local control rate and long-term survival rate. Radiotherapy has become the main technique for breast cancer treatment. How to further reduce the adverse reactions of patients’ normal tissues and improve the curative effect of radiotherapy has become the research focus. This study aimed to investigate the expressions of human epidermal growth factor receptor 2 (HER2) and breast cancer susceptibility gene 1 (BRCA1) in breast cancer patients, and to study the correlation between their expressions and radiation sensitivity, so as to provide the experimental foundation for clinical treatment research. Methods: Breast cancer tissues and adjacent normal breast tissues of 156 breast cancer patients treated in Affiliated Cancer Hospital of Zhengzhou University were collected in this retrospective cohort study, and the tissues of 145 patients with benign breast disease were selected as the control. Real-time fluorescence quantitative polymerase chain reaction (RTFQ-PCR) was used to detect the expressions of HER2 and BRCA1 in tissues. Immunohistochemistry was used to test the HER2 and BRCA1 protein expressions in tissues. Relationships of HER2 and BRCA1 expressions with radiation sensitivity and prognosis of breast cancer patients were assessed by Spearman correlation analysis and Kaplan-Meier survival analysis. Results: Compared with the adjacent normal breast tissues and benign breast lesion tissues, breast cancer tissues had high expressions of HER2 mRNA and protein and low expressions of BRCA1 mRNA and protein (P<0.01). After radiotherapy, the local failure rate of HER2 positive patients was significantly higher compared with the HER2 negative patients (P<0.05), while that of BRCA1 positive patients was significantly lower compared with the negative group (P<0.01). The survival time of HER2 positive patients was significantly shorter compared with the HER2 negative patients, while that of BRCA1 positive patients was significantly longer compared with the BRCA1 negative patients (P<0.01). Conclusion: The breast cancer patients with high HER2 gene expression and low BRCA1 gene expression are less sensitive to radiotherapy, providing a new theoretical basis for the clinical treatment of breast cancer patients.

Key words: Breast cancer, Human epidermal growth factor receptor 2, Breast cancer susceptibility gene 1, Radiation sensitivity, Local failure rate