• Primary objective: To describe event-free survival (EFS) in patients with stage I-III HR+/HER2- early breast cancer (EBC) who received curative surgery followed by systemic therapy.
• Secondary objectives: Include assessment of relapse-free survival (RFS), distant disease-free survival (DDFS), distant relapse-free survival (DRFS), overall survival (OS), site of distant recurrence, and time-to-next treatment (TTNT), as well as evaluating the association between clinicopathologic/treatment variables and clinical outcomes.
• Key inclusion criteria: Adults (≥18 years) with stage I-III HR+/HER2- invasive breast cancer who underwent curative surgery
• Key exclusion criteria: HR- or HER2+ tumors, de novo stage IV, or lack of curative-intent surgery

Inclusion Criteria:

1. Patients (female or male) with a histologically confirmed first diagnosis of invasive breast cancer, identified by International Classification of Diseases, 10th Revision (ICD-10) code C50.x, between January 1, 2010, and December 31, 2023.* The date of diagnosis will be based on the initial pathology report or the date reported to the Korea Central Cancer Registry (KCCR).
2. Age 18 years or older at the time of initial diagnosis.
3. Anatomical stage I, II, or III disease at initial diagnosis, staged according to the American Joint Committee on Cancer (AJCC) Cancer Staging Manual, using the edition contemporary to the time of diagnosis.
4. Confirmed HR-positive disease, defined as estrogen receptor (ER) and/or progesterone receptor (PR) expression in ≥1% of invasive tumor cells on immunohistochemistry (IHC), or an Allred proportion score of 2 or higher.
5. Confirmed HER2-negative disease, defined as an IHC score of 0 or 1+, or an IHC score of 2+ with a negative in situ hybridization (ISH) result (e.g., fluorescence in situ hybridization or silver in situ hybridization). Patients recorded as HER2-negative without a specific score available will also be included.
6. Documented history of having received definitive (curative-intent) surgery for the primary breast cancer (e.g., breast-conserving surgery or mastectomy).

Exclusion Criteria:

1. Patients (female or male) with a histologically confirmed first diagnosis of invasive breast cancer, identified by International Classification of Diseases, 10th Revision (ICD-10) code C50.x, between January 1, 2010, and December 31, 2023.* The date of diagnosis will be based on the initial pathology report or the date reported to the Korea Central Cancer Registry (KCCR).
2. Age 18 years or older at the time of initial diagnosis.
3. Anatomical stage I, II, or III disease at initial diagnosis, staged according to the American Joint Committee on Cancer (AJCC) Cancer Staging Manual, using the edition contemporary to the time of diagnosis.
4. Confirmed HR-positive disease, defined as estrogen receptor (ER) and/or progesterone receptor (PR) expression in ≥1% of invasive tumor cells on immunohistochemistry (IHC), or an Allred proportion score of 2 or higher.
5. Confirmed HER2-negative disease, defined as an IHC score of 0 or 1+, or an IHC score of 2+ with a negative in situ hybridization (ISH) result (e.g., fluorescence in situ hybridization or silver in situ hybridization). Patients recorded as HER2-negative without a specific score available will also be included.
6. Documented history of having received definitive (curative-intent) surgery for the primary breast cancer (e.g., breast-conserving surgery or mastectomy).

Key inclusion criteria: Adults (≥18 years) with stage I-III HR+/HER2- invasive breast cancer who underwent curative surgery Key exclusion criteria: HR- or HER2+ tumors, de novo stage IV, or lack of curative-intent surgery

It will be decided later.