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

This study will recruit 168 patients in approximately 20 study centres in China. This open label, randomised, parallel group, multicentre study in Chinese pre menopausal patients with ER+/HER2- early breast cancer will be conducted to determine whether 3 monthly ZOLADEX 10.8 mg injection is non-inferior to monthly ZOLADEX 3.6 mg injection in terms of estradiol (E2) suppression. The study will also assess the PK, pharmacodynamics (PD), safety and tolerability of two difference strengths of ZOLADEX. Eligible patients, as judged by the Investigator after completion of the screening tests, will be registered for this study and at the same time randomised in a 1:1 ratio to receive one of the following treatments. The study treatment must start within 7 days after randomisation. * ZOLADEX 10.8 mg depot group: subcutaneous depot injection once every 12 weeks * ZOLADEX 3.6 mg depot group: subcutaneous depot injection once every 4 weeks The primary objective: \- To examine whether ZOLADEX 10.8 mg depot is non-inferior to ZOLADEX 3.6 mg depot in terms of the suppression rate of serum estradiol (E2) to the menopausal level (≤30 pg/mL) from Week 4 through Week 24. The secondary objectives: * To evaluate the safety and tolerability profiles of ZOLADEX 10.8 mg depot and ZOLADEX 3.6 mg depot. * To evaluate the estradiol (E2) suppression by assessment of area under the curve (AUC) of E2 serum concentration during the 24 weeks of treatment. * To evaluate the goserelin pharmacokinetics (PK) in Chinese patients after injection of ZOLADEX 10.8 mg depot and ZOLADEX 3.6 mg depot. * To assess the influence on menstruous condition after injection of ZOLADEX 10.8 mg depot or ZOLADEX 3.6 mg depot. * To assess the hormonal conditions after injection of ZOLADEX 10.8 mg depot compared with ZOLADEX 3.6 mg depot.