This non-interventional retrospective study will describe real-world treatment patterns and clinical outcomes among adults with HER2-negative metastatic breast cancer with germline BRCA1/2 mutations who initiated talazoparib as a first or later line of therapy. Patients will be identified from the Flatiron Electronic Health Record database.

Inclusion Criteria:

Patients must meet all of the following inclusion criteria to be eligible for inclusion in the study:

• Diagnosed with breast cancer (ICD-9 174.x or 175.x or ICD-10 C50x)
• At least two visits in the Flatiron database on or after January 1, 2011
• Pathology consistent with breast cancer
• Has evidence of stage IV or recurrent metastatic breast cancer with a metastatic diagnosis date on or after January 1, 2011. This includes patients who were diagnosed with stage IV at diagnosis or were diagnosed with earlier stage disease, then developed a distant metastasis later on, or had recurrence of the disease via a distant metastasis
• Confirmed receipt of talazoparib as treatment for mBC via abstraction initiated between January 1, 2018 and September 30, 2020
• HER2 negative test result on or before the start of patient's first talazoparib-containing line of therapy, as defined by Flatiron's line of therapy rules
• BRCA1, BRCA2, BRCA1 and BRCA2 germline mutation, or BRCA germline mutation not otherwise specified, identified on or before the start date of patient's first talazoparib-containing line of therapy, as defined by Flatiron's line of therapy business rules
• Age 18 years or older at the time of first talazoparib-containing line of therapy

Exclusion Criteria:

• Lacking relevant unstructured documents in the Flatiron database for review by the abstraction team
• Receipt of drug as part of a clinical trial (captured in the database as "clinical study drug" without additional information about active ingredient or whether the patient received placebo), defined as any non-cancelled order, administration, or oral episode for a drug used in a clinical trial, on or prior to start of first talazoparib line of therapy, as defined by Flatiron's line of therapy business rules

Adult patients with HER2-negative metastatic breast cancer with germline BRCA1/2 mutations who initiated talazoparib treatment in first-line or later line of therapy between January 1, 2018 and September 30, 2020 identified from Flatiron Health Analytic Database.

Pfizer will provide access to individual de-identified participant data and related study documents (e.g. protocol, Statistical Analysis Plan (SAP), Clinical Study Report (CSR)) upon request from qualified researchers, and subject to certain criteria, conditions, and exceptions. Further details on Pfizer's data sharing criteria and process for requesting access can be found at: https://www.pfizer.com/science/clinical\_trials/trial\_data\_and\_results/data\_requests.

Full Analysis Set included adult participants with HER2-negative mBC with gBRCA1/2 mutations who initiated talazoparib treatment in first-line or later identified from Flatiron Health Analytic Database.

Not applicable as adverse events were not planned to be collected during the study

Minimum criteria for reporting an adverse event (i.e. identifiable participant, identifiable reporter, a suspect product, and event) could not be met. Hence, adverse events were not collected and reported.