Inclusion Criteria:
1. Diagnosed with HR+/HER2- ABC:
HR+ is defined as ER+ or PR+, and HER2+ is defined as immunohistochemistry 3+, or 2+ with positive in situ hybridization (amplification). Advanced or metastatic breast cancer is defined as having a documented inoperable clinical or pathological stage IIIB, IIIC, or IV, or the records indicating distant metastasis.
2. Initiation of 1L anti-cancer treatment between Jan. 1, 2024 and Jan. 1, 2027; Defined as having records of systemic anti-cancer treatment in disease course records or order records within 90 days after the initial diagnosis of ABC, and receiving the first dose between Jan. 1, 2024 and Jan. 1, 2027, as recorded in the NATDSS database.
3. Aged 18 years or older at the time of receiving the 1L treatment; Definition: The initiation date (index date) of 1L treatment is defined as the initiation date of systemic anti-cancer treatment for HR+/HER2- ABC first recorded in the database. Age will be preferentially calculated based on the date of birth (or year of birth) and the initiation date of 1L treatment in the database. If the birth information is not included in the database but shown in an "Age" field in the medical visit/hospitalization record associated with 1L treatment, this age field will be used as the basis for age.
4. At least 3 months of follow-up records after the initiation of 1L treatment. Defined as having at least one outpatient or inpatient medical visit record in the NATDSS at least 3 months after the index date.
Exclusion Criteria:
(1) Patients with any other concomitant invasive malignancies Defined as patients meeting any of the following conditions based on their diagnosis records in the cancer registry/medical database used for the study: 1. Within 5 years before the diagnosis of HR+/HER2- ABC, there is a diagnosis record of invasive malignancy other than breast cancer in the database (based on the International Classification of Diseases \[ICD\] diagnosis code or cancer registry code), and the diagnosis is not carcinoma in situ or benign/borderline tumor; 2. On the day of, or within 3 months after, the diagnosis of HR+/HER2- ABC, there is a new diagnosis record of invasive malignancy at another site (also based on the ICD diagnosis code or cancer registry code) indicating a concomitant active malignancy.
