A Real-World Study of Treatment Patterns, Tolerability and Effectiveness of CDK4/6 Inhibition in HR+, HER2-negative Metastatic Breast Cancer Patients

Inclusion Criteria:

1. Included in Flatiron's mBC Enhanced Data Model (EDM):

   1. Had an International Classification of Diseases (ICD) diagnosis of breast cancer (ICD, 9th revision, clinical modification \[ICD-9-CM\] 174.x or 175.x or ICD, 10th revision, clinical modification \[ICD-10-CM\] C50x)
   2. At least two documented clinical visits, on different days, occurring on or after January 1, 2011
   3. Included in probabilistic sample of patients queued for review via abstraction
   4. Had pathology consistent with breast cancer
   5. Had evidence of stage IV or recurrent mBC with a metastatic diagnosis date on or after January 1, 2011, including patients diagnosed as stage IV at initial diagnosis, or diagnosed with earlier stage disease who then developed metastatic disease
2. Initiated treatment with first-line (1L) ribociclib (in combination with endocrine therapy \[ET\]) in the metastatic setting on or after January 1, 2018, and at least 6 months prior to the study data cutoff date (October 31, 2024) to ensure adequate time to observe dose modifications and treatment discontinuations
3. Had evidence of HR+/HER2- test result prior to or up to 30 days after initiation of 1L ribociclib
4. Had 1L ribociclib on or before April 30, 2024, to allow for at least 6 months of potential follow-up time prior to the data cutoff date of October 31, 2024

Exclusion Criteria:

1. Use of any CDK4/6 inhibitor therapy in combination with tamoxifen
2. Use of any CDK4/6 inhibitor in the pre-metastatic setting