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.

Inclusion Criteria:

1. Female, aged 18-60
2. Premenopausal patients with early hormone receptor-positive breast cancer at intermediate to high risk (Low risk is defined as having the following 6 items at the same time: lesion size (pT) in the specimen <= 2cm; histological grade 1; no vessel carcinoma embolus; ER and/or PR positive; HER2 gene without overexpression or amplification; age >=35 years old)
3. Completed radical surgery for breast cancer
4. Undergoing postoperative endocrine therapy (toremifene, tamoxifen, aromatase inhibitorI) at least five years at Sun Yat-sen Memorial Hospital of Sun Yat-sen University since 2010
5. Undergoing ovarian function suppression (Oophorectomy, Ovarian irradiation, Gonadotropin-releasing hormone agonist)

Exclusion Criteria:

1. Imaging or pathology suggestive of metastatic breast cancer (chest wall, lung, bone, liver, brain)
2. Patients with a second primary tumor
3. Hepatic insufficiency at baseline
4. Known history of psychotropic substance abuse or drug abuse;

1. Female, age ≥ 18
2. Premenopausal patients with early hormone receptor-positive breast cancer at intermediate to high risk (Low risk is defined as having the following 6 items at the same time: lesion size (pT) in the specimen <= 2cm; histological grade 1; no vessel carcinoma embolus; ER and/or PR positive; HER2 gene without overexpression or amplification; age >=35 years old)
3. Completed radical surgery for breast cancer
4. Undergoing postoperative endocrine therapy (toremifene, tamoxifen, aromatase inhibitorI) at least five years at Sun Yat-sen Memorial Hospital of Sun Yat-sen University since 2010
5. Undergoing ovarian function suppression (Oophorectomy, Ovarian irradiation, Gonadotropin-releasing hormone agonist)