This Clinical Trial is a Retrospective, Multicenter Cohort Study Evaluating the Real-world Characteristics and Risk of Disease Recurrence in Hormone Receptor-positive, HER2-negative Early Breast Cancer.

Inclusion criteria

• ✓. 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).
• ✓. Age 18 years or older at the time of initial diagnosis.
• ✓. 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.
• ✓. 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.
• ✓. 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.
• ✓. Documented history of having received definitive (curative-intent) surgery for the primary breast cancer (e.g., breast-conserving surgery or mastectomy).

Exclusion criteria