Real-World Outcomes of Patients With Metastatic Breast Cancer After Treatment With First-Line ET+CDK4/6i

Inclusion criteria * Patients with evidence of Stage IV or recurrent mBC with a metastatic diagnosis date on or after January 1, 2017 * Aged ≥18 years at mBC diagnosis date * Received 1L ET + CDK 4/6i, with no other systemic agents, in the metastatic setting * Had evidence of a rwP event during 1L ET + CDK 4/6i * Evidence of a subsequent LOT following 1L ET + CDK 4/6i (start date of subsequent LOT = index treatment date) * A record of HR+ status in the closest estrogen receptor (ER) or progesterone receptor (PR) test result occurring prior to or within 30 days after the index treatment date * A record of HER2- status in the closest HER2 test result recorded prior to or on the index treatment date * Index treatment date occurring at least 90 days prior to end of study period (30Sep2024) Exclusion Criteria • A record of estrogen receptor 1 (ESR1), phosphatidylinositol4,5-bisphosphate 3-kinase catalytic subunit alpha (PIK3CA), V-akt murine thymoma viral oncogene homolog (AKT1), phosphatase and tensin homolog (PTEN), or germline breast cancer gene (gBRCA) alteration/mutation prior to or within 30 days after index treatment date