European Treatment Patterns and Outcomes Associated With First-Line CDK4/6 Inhibition and Hormonal Therapies

Inclusion Criteria:

* Is male or female
* Has histologically or cytologically confirmed breast cancer diagnosis (HR+/HER2- breast cancer)
* Has received a diagnosis of locally advanced breast cancer not amenable to curative radiation or surgical cure or of metastatic breast cancer (i.e., advanced breast cancer \[ABC\]); diagnosis may be de novo (initial diagnosis at ABC stage) or recurrent from earlier-stage disease (initial diagnosis of earlier-stage disease with subsequent progression to advanced disease)
* Has initiated a required first-line therapy of interest: Palbociclib plus AI as first-line therapy for ABC between September 1, 2016, and July 31, 2020, or AI monotherapy as first-line therapy for ABC between January 1, 2010,, and July 31, 2020
* Was aged 18 years or older at the time of diagnosis of ABC
* Is living or deceased at the time of record abstraction
* Has a complete medical record, covering treatment for ABC, including any transfer record from other facilities (if applicable) that is available to the abstractor for data abstraction

Exclusion Criteria:

* The patient's first treatment after ABC diagnosis was chemotherapy (including induction chemotherapy)
* The patient has evidence of other active malignant neoplasms within 3 years (except nonmelanoma skin cancer or carcinoma in situ) prior to diagnosis of ABC; patients diagnosed with second primary cancer after ABC diagnosis will not be excluded
* The patient has evidence of prior treatment with any CDK4/6 inhibitor (i.e. palbociclib, abemaciclib, ribociclib) in the early-stage breast cancer setting or treatment with abemaciclib or ribociclib in the ABC setting
* The patient has participated in a clinical trial related to treatment of ABC (including after first-line therapy \[i.e., palbociclib plus AI or AI monotherapy\])