This is a multi-center, retrospective-prospective, observational, active-control, non-inferiority, real world study using hospital medical record data, with objectives to evaluate E2 suppressive effect of Zoladex® 10.8 mg is non-inferior to Zoladex® 3.6 mg. Eligible breast cancer patients who received Zoladex® from January 1st, 2015 till December 31st, 2021(including December 31st, 2021) will be identified and included for retrospective data collection and analyses in this study. And prospective data will be monthly collected of eligible patients receiving Zoladex® after January 1st, 2022 (including January 1st, 2022) until approximately 1000 patients being included in this study for analysis. (If site has specific identification of retrospective data and prospective data, it will be subject to the requirement of site). The first date of the presence of Zoladex® treatment or prescription record for breast cancer during the study period will be considered the index date for patients. According to the Zoladex® treatment at the index date, patients will be categorized into two cohorts: Zoladex® 10.8 mg or Zoladex® 3.6 mg.

About 10-15 hospitals will be included in this study. To be considered, the hospitals need to have relatively large number of eligible patients, geographic representativeness and willingness to participate in this study. Approximately 1000 eligible patients from selected hospitals during the study period will be included and matched with propensity scores. It is expected that at least 150 matched patients in each of the two cohorts will eventually be included in the primary endpoint analysis. The final subject number will be based on the actual situation of the study.

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 treatment of Zoladex®. Baseline premenopausal status will be confirmed if the patient's last E2 measurement within 180 days prior to the index date indicated premenopausal status or there was a recorded menstrual history within 180 days prior to the index date
• At least one actual or expected E2 testing measurement within 8-28 weeks of the index date Exclusion Criteria
• Patients received concurrent treatments that may affect E2 testing results

Patients with premenopausal and perimenopausal breast cancer