Clinical Research Directory

Inclusion Criteria: Step 1：iOFS detection phase 1. Female, aged ≥18 and ≤45 years; 2. Histologically confirmed hormone receptor-positive (HR+) (estrogen receptor \[ER\] and/or progesterone receptor \[PR\] ≥1%) and human epidermal growth factor receptor 2-negative (HER2-) early invasive breast cancer (stage I-III according to the American Joint Committee on Cancer \[AJCC\], version 8)； 3. Completed curative surgery, with prior (neo)adjuvant chemotherapy and radiotherapy completed if applicable; 4. Currently receiving adjuvant therapy with a 3-month GnRH agonist (GnRHa) plus aromatase inhibitor (AI) or tamoxifen (TAM), with or without CDK4/6 inhibitors (excluding abemaciclib due to its potential interference with estradiol monitoring), for ≥1 dose, and presenting with estradiol (E2) ≥30 pg/mL within 28 days prior to enrollment (measured by CLIA). 5. Eastern Cooperative Oncology Group (ECOG) performance status score of 0-1; adequate bone marrow, hepatic, renal, and cardiac function. 6. Voluntarily sign a written informed consent form before the trial screening. Step 2：Randomized treatment phase 1. iOFS confirmed using the SEMS assay (E2 ≥30 pg/mL); 2. Ongoing adjuvant therapy with a 3-month GnRHa plus AI or TAM, with or without CDK4/6 inhibitors. 3. No evidence of disease progression. Exclusion Criteria: Step 1：iOFS detection phase 1. Bilateral breast cancer, inflammatory breast cancer, or distant metastasis; 2. Use of GnRHa for ovarian function preservation; 3. History of ovarian resection or ablation; planned pregnancy or breastfeeding; 4. Concomitant use of hormonal agents other than estrogen, progesterone, selective estrogen receptor modulators (SERM), or selective estrogen receptor degraders (SERD); 5. Severe uncontrolled comorbidities; 6. Other malignancies within the past 5 years (except for curatively treated carcinoma in situ of the cervix or basal cell carcinoma); 7. Failure to comply with follow-up or psychiatric disorders. Step 2：Randomized treatment phase a)Prior conversion from a 3-month GnRHa to a 1-month GnRHa.