This study aims to enroll premenopausal patients, with early breast cancer who are non-low-risk and hormone receptor-positive and have undergone prior surgical intervention at the Breast Cancer Center of Sun Yat-sen Memorial Hospital, Sun Yat-sen University. These participants, receiving tamoxifen (TAM), toremifene (TOR), or aromatase inhibitors (AI) as adjuvant endocrine therapy and undergoing ovarian function suppression (OFS) treatment, will be divided into three groups, namely TOR+OFS, TAM+OFS, AI+OFS. The study will compare the efficacy and safety of TOR+OFS to that of TAM+OFS or AI+OFS in premenopausal estrogen receptor-positive breast cancer patients by comparing the 5-year disease-free survival (DFS) and quality of life etc. The objective is to evaluate whether TOR+OFS is non-inferior to TAM+OFS or AI+OFS in this specific patient population.

Selective estrogen receptor modulators (SERM), tamoxifen (TAM) and toremifene (TOR), have been proven to be effective in premenopausal estrogen receptor positive breast cancer patients with similar outcomes. In addition, many large-scale long-term follow-up clinical tials, such as ABCSG XII, SOFT, TEXT, ASTRRA, and ZIPP, have confirmed that premenopausal patients with hormone-receptor-positive breast cancer at intermediate to high risk could benefit from ovarian function suppression (OFS) combined with aromatase inhibitor (AI) or TAM. The Asian Breast Cancer Cooperative Group (ABCCG) also recommends OFS+TAM or OFS+AI for the treatment in this specific patient population. Notably, the therapeutic efficacy and safety profile of OFS in conjunction with TOR have yet to be investigated, nor has its comparative effectiveness with OFS plus TAM or OFS plus AI been established. This study aims to enroll premenopausal patients, with early breast cancer who are non-low-risk and hormone receptor-positive and have undergone prior surgical intervention at the Breast Cancer Center of Sun Yat-sen Memorial Hospital, Sun Yat-sen University. These participants, receiving tamoxifen (TAM), toremifene (TOR), or aromatase inhibitors (AI) as adjuvant endocrine therapy and undergoing ovarian function suppression (OFS) treatment, will be divided into three groups, namely TOR+OFS, TAM+OFS, AI+OFS. The study will compare the efficacy and safety of TOR+OFS to that of TAM+OFS or AI+OFS in premenopausal estrogen receptor-positive breast cancer patients by comparing the 5-year disease-free survival (DFS) and quality of life etc. The objective is to evaluate whether TOR+OFS is non-inferior to TAM+OFS or AI+OFS in this specific patient population.