Description of Treatment Patterns and Description and Comparison of Healthcare Resource Utilization and Costs of Women With Metastatic HR+/HER2- Breast Cancer Treated With CDK4/6 Inhibitors

Inclusion Criteria:

\- Evidence of treatment with a CDK4/6 inhibitor regardless of the line of therapy.

The initiation of the first CDK4/6 inhibitor was defined as the index date, and the first CDK4/6 inhibitor initiated was defined as the index treatment

* BC diagnosis: Two diagnosis codes of BC (International Classification of Diseases, 9th Revision, Clinical Modification \[ICD-9-CM\]: 174.xx and International Classification of Diseases, 10th Revision, Clinical Modification \[ICD-10-CM\]: C50.xx \[excluding C50.x2 - male BC\]) on two medical service claims separated by at least 30 days
* Metastatic disease diagnosis: At least two medical claims for a secondary neoplasm (ICD-9-CM codes: 196.xx-197.xx, 198.xx, ICD-10-CM codes: C77.xx, C78.xx, C79.xx) on separate dates, with the first one occurring no more than 30 days before the first diagnosis for BC
* HR+/HER2-: At least one prescription fill or administration of an ET (anastrazole, exemestane, ethinyl estradiol, fulvestrant, fluoxymesterone, letrozole, megestrol acetate, tamoxifen, or toremifene), HR+/HER2- therapy (everolimus), or CDK4/6 inhibitor (i.e., abemaciclib, palbociclib, or ribociclib) at any time following the diagnosis of BC, and no claims for treatments indicated for HER2+ BC, including trastuzumab, lapatinib, afatinib, pertuzumab, or ado-trastuzumab, at any time in the data period
* Women of at least 18 years of age as of the index date
* At least 6 months of continuous health plan coverage prior to and at least 1 month of continuous health plan coverage after the index date

Exclusion Criteria:

* None