The goal of this observational study is to observe the long-term prognosis of patients with early HR-positive premenopausal breast cancer. The study also aims to understand the compliance with and reasons for discontinuing adjuvant OFS endocrine therapy under different combination regimens.

The main questions it aims to answer are:

1. What are the rates of compliance with and reasons for discontinuation of adjuvant OFS endocrine therapy?
2. What is the impact of OFS treatment duration on patient prognosis?

Participants, who are already receiving OFS treatment as part of their regular medical care, will have their demographic data, treatment status, clinical outcomes, and adverse events collected over time.

This real-world non-interventional prospective study aims to explore the compliance and reasons for discontinuation of adjuvant OFS endocrine therapy in early HR-positive premenopausal breast cancer patients under different combination regimens of adjuvant endocrine drugs, as well as to observe the impact of the duration of OFS treatment on prognosis. This study adopts a multi-center, prospective, non-interventional design to collect approximately 300 cases of early HR-positive premenopausal breast cancer patients who received OFS treatment. After obtaining informed consent, the demographic data, breast cancer diagnosis information, comorbidities, past medical history, treatment status, clinical outcomes, and adverse events of the patients were collected. The patients were administered medication in accordance with the standard clinical drug protocols and completed follow-up according to the follow-up plan.

Inclusion Criteria:

1. Female breast cancer patients who were premenopausal at the time of surgery.
2. Newly diagnosed patients with invasive breast cancer, tumor node metastasis(TNM) stage I-III.
3. HR-positive (defined as ER ≥ 10% and/or progesterone receptor(PR) ≥ 10%).
4. Patients who have undergone radical mastectomy and are planning to receive OFS treatment.
5. Have received (neo)adjuvant chemotherapy and radiotherapy.
6. Eastern Cooperative Oncology Group Performance Status(ECOG PS) score of 0-1.
7. Complete medical records.
8. Willing to accept long-term follow-up.
9. Any adverse events that occurred during adjuvant chemotherapy (if applicable) have recovered or decreased to grade 1 (according to CTCAE v5.0) at the start of OFS treatment.

Exclusion Criteria:

1. Simultaneously participating in another blinded clinical study.
2. Presence of other active malignant tumors or multiple primary cancers.
3. Pregnant or lactating women.
4. Other conditions that the investigator deems unsuitable for inclusion in the study.
5. Planning to use systemic therapies not described in the study cohort during the endocrine therapy phase (such as, but not limited to, chemotherapy, Antibody-Drug Conjugates(ADCs), or immunotherapy).

1. Female breast cancer patients who were premenopausal at the time of surgery.
2. Newly diagnosed patients with invasive breast cancer, TNM stage I-III.
3. HR-positive (defined as ER ≥ 10% and/or PR ≥ 10%).
4. Patients who have undergone radical mastectomy and are planning to receive OFS treatment.
5. Have received (neo)adjuvant chemotherapy and radiotherapy.
6. ECOG PS score of 0-1.
7. Complete medical records.
8. Willing to accept long-term follow-up.
9. Any adverse events that occurred during adjuvant chemotherapy (if applicable) have recovered or decreased to grade 1 (according to CTCAE v5.0) at the start of OFS treatment.