Statement: Females over the age of 18, whose last period was 2 weeks prior are eligible for the primary trial.
Primary_evidence: Inclusion Criteria:   Female 20 years and pre-menopausal.Pre-menopausal defined as 1) last menses within 1 year of randomisation, and 2) E2 10 pg/mL and FSH  30 mIU/mL within 4 weeks of randomisation.   Hormone sensitivity (ER positive) of primary or secondary tumour tissue.   Histological/cytological confirmation of breast cancer and are candidates to receive hormonal therapy as therapy for advanced breast cancer. Exclusion Criteria:   Patients who have received tamoxifen or other hormonal therapies as adjuvant therapy for breast cancer within 24 weeks before randomisation and/or who have received prior treatment with hormonal therapies for advanced breast cancer   Patients who have received LHRHa as adjuvant therapy for breast cancer within 48 weeks before randomisation   Patients who have relapsed during adjuvant hormonal therapy or within 48 weeks after completion of adjuvant hormonal therapy and/or