Statement: Men are not eligible for the primary trial.
Primary_evidence: Inclusion Criteria:   Premenopausal, estrogen receptor positive women, aged 20 years and over, with operable and measurable breast cancer who have provided written informed consent Exclusion Criteria:   Medical history of chemotherapy or endocrine therapy for breast cancer, or with treatment history of radiotherapy. Unwillingness to stop taking any drug known to affect sex hormone status (including hormone replacement therapy (HRT).