A Real-life Study to Understand the Use and Effects of Palbociclib in US Patients With Breast Cancer

Palbociclib Treatment Patterns and Outcomes in HR+/HER2- MBC: Flatiron Database Analysis

Palbociclib, the first oral CDK4/6 inhibitor, is an approved medicine indicated for the treatment of a kind of advanced/metastatic breast cancer (MBC), called hormone receptors positive (HR+)/ Human epidermal growth factor receptor 2 negative (HER2-) disease. Palbociclib is given orally in combination with hormonal therapies.

The purpose of this study is to better understand how Palbociclib combination is used in real-life conditions and its clinical impact compared with hormonal therapy. The study will also evaluate how long patients take the different CDK 4/6 inhibitor drugs and whether using those drugs impacts the use of chemotherapy later.

Male and female patients aged 18 years old or more presenting the following conditions will be selected for the study:

• HR+/HER2- MBC
• First treatment with Palbociclib, hormonal therapy, or other CDK4/6 inhibitors after MBC diagnosis The study will use data without personal identity, which were obtained from medical records in routine clinical practice.

Study Overview

• Status: Active, not recruiting
• Conditions: Breast Cancer; Malignant Neoplasm of Breast
• Intervention / Treatment: Drug: Palbociclib; Drug: Abemaciclib; Drug: Aromatase inhibitor; Drug: Ribociclib

• Study Type: Observational
• Enrollment (Estimated): 1

Contacts and Locations

Study Locations

• United States
  • New York
    • New York, New York, United States, 10001
      • Pfizer New York

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult; Older Adult
• Accepts Healthy Volunteers: No

• Sampling Method: Probability Sample

Study Population

Flatiron Health Database is a longitudinal, demographically, and geographically diverse dataset derived from EHR data from over 280 cancer clinics (~800 sites of care) including more than 3.0 million active US cancer patients available for analysis. This study uses secondary de-identified Flatiron Health data that involve men and women who had been diagnosed with HR+/HER2-MBC in the United States.

Description

Patients are eligible for the study if they were 18 years of age or older at MBC diagnosis, had HR+/HER2- confirmed and initiated first line therapy (CDK4/6i, ET, CT, or other) in the metastatic setting during the period from February 2015 through June 2022 or data cutoff.

Study Plan

How is the study designed?

Number of groups / cohorts

4

Cohorts and Interventions

Group / Cohort	Intervention / Treatment
Palbociclib + aromatase inhibitor (AI); Oral palbociclib + AI combination treatment regimen as decided by physician	Drug: Palbociclib; CDK4/6 inhibitor; Other Names: Ibrance; Drug: Aromatase inhibitor; Aromatase inhibitor; Other Names: a class of drugs included in the study: letrozole (Femara), anastrozole (Arimidex), and exemestane (Aromasin)
Aromatase inhibitor (AI); Oral AI treatment regimen as decided by physician	Drug: Aromatase inhibitor; Aromatase inhibitor; Other Names: a class of drugs included in the study: letrozole (Femara), anastrozole (Arimidex), and exemestane (Aromasin)
Abemaciclib plus aromatase inhibitor (AI); Oral abemaciclib plus AI treatment regimen as decided by physician	Drug: Palbociclib; CDK4/6 inhibitor; Other Names: Ibrance; Drug: Abemaciclib; CDK4/6 inhibitor; Other Names: Verzenio; Drug: Aromatase inhibitor; Aromatase inhibitor; Other Names: a class of drugs included in the study: letrozole (Femara), anastrozole (Arimidex), and exemestane (Aromasin)
Ribociclib plus aromatase inhibitor (AI); Oral ribociclib plus AI as decided by physician	Drug: Aromatase inhibitor; Aromatase inhibitor; Other Names: a class of drugs included in the study: letrozole (Femara), anastrozole (Arimidex), and exemestane (Aromasin); Drug: Ribociclib; CDK4/6 inhibitor; Other Names: Kisqali

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Time Frame
Overall Survival (OS)	From start of index line of therapy to death, February 2015 - December 2022 or data cutoff

Secondary Outcome Measures

Outcome Measure	Time Frame
Real Progression Free Survival (rwPFS)	From start of index line of therapy to death or disease progression, February 2015 - December 2022 or data cutoff
Progression Free Survival 2	from start of index treatment to disease progression on the 2nd line of therapy or death, February 2015 - December 2022 or data cutoff
Real-World Tumor Response (rwTR)	From start of index treatment to tumor response, February 2015 - December 2022 or data cutoff
Duration of treatment	from index treatment initiation to end of the treatment, February 2015 - December 2022 or data cutoff
Time to chemotherapy	from index treatment initiation to subsequent chemotherapy, February 2015 - December 2022 or data cutoff

Other Outcome Measures

Outcome Measure	Time Frame
Early discontinuation	from index treatment initiation to discontinuation between February 2015 - December 2022 or data cutoff
Dose adjustment	from index treatment initiation to initial dose change, February 2015 - December 2022 or data cutoff

Collaborators and Investigators

• Sponsor: Pfizer
• Investigators: Study Director: Pfizer CT.gov Call Center, Pfizer

Publications and helpful links

General Publications

• Lynce F, Liu X, Li B, McRoy L, Chen C, Liu R, Rugo HS. Real-world effectiveness of palbociclib plus an aromatase inhibitor in HR+/HER2- MBC patients living in disadvantaged neighborhoods. NPJ Breast Cancer. 2025 Jul 21;11(1):75. doi: 10.1038/s41523-025-00786-z.

Helpful Links

• To obtain contact information for a study center near you, click here.

Study record dates

Study Major Dates

• Study Start (Actual): June 24, 2024
• Primary Completion (Estimated): December 30, 2026
• Study Completion (Estimated): December 30, 2026

Study Registration Dates

• First Submitted: July 3, 2024
• First Submitted That Met QC Criteria: July 3, 2024
• First Posted (Actual): July 10, 2024

Study Record Updates

• Last Update Posted (Actual): November 25, 2025
• Last Update Submitted That Met QC Criteria: November 22, 2025
• Last Verified: November 1, 2025

More Information

Terms related to this study

• Keywords: Metastatic breast cancer; Overall survival; Palbociclib; Real-world data; CDK4/6 inhibitor; Retrospective observational study
• Additional Relevant MeSH Terms: Neoplasms by Site; Neoplasms; Skin Diseases; Breast Diseases; Skin and Connective Tissue Diseases; Breast Neoplasms; Physiological Effects of Drugs; Molecular Mechanisms of Pharmacological Action; Hormones, Hormone Substitutes, and Hormone Antagonists; Enzyme Inhibitors; Steroid Synthesis Inhibitors; Hormone Antagonists; Estrogen Antagonists; Organic Chemicals; Heterocyclic Compounds, 1-Ring; Heterocyclic Compounds; Azoles; Pharmacologic Actions; Chemical Actions and Uses; Nitriles; Triazoles; Letrozole; Anastrozole; Aromatase Inhibitors; abemaciclib; ribociclib; palbociclib; exemestane
• Other Study ID Numbers: A5481189; NCT06495164 (Registry Identifier: ClinicalTrials.gov)

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO
• IPD Plan Description: 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.

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: Yes
• Studies a U.S. FDA-regulated device product: No