To Compare ZOLADEX 10.8 mg With ZOLADEX 3.6mg in Chinese Pre-menopausal ER+ HER2- Early Breast Cancer.

Inclusion Criteria:

1. Provision of informed consent prior to any study specific procedures.
2. Women aged ≥18 at screening, in pre-menopausal status defined as:

• Menses within 1 year before enrolment and within 3 weeks before enrolment, E2 >30pg/mL and FSH ≤40 mIU/mL.
• Patients who received neo/adjuvant chemotherapy before randomisation should nothaving chemical menopause (Patients should meet: E2>30pg/mL and FSH ≤40mIU/mL)within 12 weeks after completion of the postoperative chemotherapy.

3. Histologically confirmed ER+/HER2- primary invasive operable breast cancer (ER+defined as at least 1% of the cells examined by immunohistochemistry testing haveestrogen receptors).
4. Neoadjuvant chemotherapy and adjuvant chemotherapy prior to study enrolment areacceptable. (Please refer to Guidelines such as NCCN Clinical practice guidelines inoncology-breast cancer and CSCO-BC breast cancer guidelines for standard protocols anddosages. Please make accurate records.).
5. Have had proper surgery for primary breast cancer with no known clinical residual locoregional disease.
6. World Health Organization (WHO) performance status of 0, 1, or 2.
7. Female patients of child bearing potential and their partners, who are sexuallyactive, must agree to the use of two highly effective forms of contraception incombination throughout the period of taking study treatment and for at least 3 monthafter last dose of Zoladex or Tamoxifen which happens later, or they musttotally/truly abstain from any form of sexual intercourse.

Exclusion Criteria:

1. Any evidence of metastatic disease.
2. Have received other previous neo/adjuvant endocrine therapy for breast cancer.
3. Other malignancy within the last 3 years except adequately treated basal cell/squamouscell carcinoma of the skin or cancer of the cervix.
4. Have any unstable complication or uncontrolled infection during screening.
5. Patients considered at poor medical risk due to a serious, uncontrolled medicaldisorder, non malignant systemic disease or active, uncontrolled infection. Examplesinclude, but are not limited to, uncontrolled ventricular arrhythmia, recent (within 3months) myocardial infarction, uncontrolled major seizure disorder, extensivebilateral lung disease on High Resolution Computed Tomography scan or any psychiatricdisorder that prohibits obtaining informed consent.
6. Postmenopausal woman, defined as a woman fulfilling any of the following criteria:

• Having undergone a bilateral oophorectomy
• Age ≥60 years
• Age <60 years and amenorrheic for 12 or more months in the absence ofchemotherapy, tamoxifen, toremifene or ovarian suppression and FSH and oestradiollevel in the postmenopausal range (utilising ranges from the local laboratoryfacility)
• If taking tamoxifen or toremifene, and age < 60 years, then FSH and plasmaoestradiol level in the postmenopausal ranges (utilising ranges from the locallaboratory facility)

7. Have had a bilateral oophorectomy or ovarian irradiation.
8. HER2 overexpression or gene amplification, i.e., immunohistochemistry (IHC)3+ orfluorescence in situ hybridisation (FISH)+, where appropriate
9. Screening test results of:

• Platelets <100 × 109/L
• Total bilirubin >1.5 × upper limit reference range (ULRR)
• Alanine aminotransferase (ALT) or Aspartate aminotransferase (AST) >2.5 × ULRR

10. Any other significantly abnormal laboratory test result at screening that would placethe patient at unusual risk or confound the results of the study.
11. Patients with a relevant history of any severe concomitant disease that would placethe patient at unusual risk or confound the results of the study, e.g., a strongfamily history of osteoporosis or severe renal or hepatic impairment.
12. Patients who, for whatever reason (e.g., confusion, infirmity, alcoholism) areunlikely to comply with study requirements as judged by the Investigator(s).
13. Patients considered by the Investigator(s) to be at risk of transmitting any infectionthrough blood or other body fluids including the agents for acquired-immune deficiencysyndrome (AIDS) or other sexually transmitted disease or hepatitis.
14. History of bleeding diathesis (i.e., disseminated intravascular coagulation [DIC] orclotting factor deficiency) or long-term anti-coagulant therapy (other than antiplatelet therapy and low dose warfarin).
15. History of any hypersensitivity to active or inactive excipients of LHRH agonist ortamoxifen.
16. Patients unwilling to stop taking any drug that affects sex hormonal status, or inwhom it would be inappropriate to stop.
17. Participation in another clinical study with an investigational product during thelast 30 days.
18. Involvement in the planning and/or conduct of the study (applies to both AstraZenecastaff and/or staff at the study centre).
19. Previous enrolment or randomisation of treatment in the present study.
20. Female patients who are pregnant or breast-feeding.