Inclusion Criteria:  Diagnosed with primary breast cancer Female，≥18 years old (at index date) HR positive Receive Zoladex® 10.8 mg or Zoladex® 3.6 mg treatment Premenopausal status prior to the injection of Zoladex®. Baseline premenopausal status will be confirmed if the patient's last E2 measurement within 180 days prior to the index date indicated as premenopausal status or there was a recorded menstrual history within 180 days prior to the index date At least one E2 test within 8-28 weeks of the index date  Exclusion Criteria:  • Patients received concurrent treatments that may affect E2 testing results