Please note that this summary only contains information from the full scientific abstract: View ESMO Scientific Abstract

A real-world study of palbociclib plus aromatase inhibitors in women with advanced breast cancer in the United States

Date of summary: September 2019

A retrospective analysis of electronic medical records between February 2015 through November 2018


The full title of this abstract is: Palbociclib plus an aromatase inhibitor as first-line therapy for metastatic breast cancer in US clinical practices: Real-world progression-free survival analysis

This study drug is approved to treat the condition under study that is discussed in this summary.


Researchers must look at the results of many types of studies to understand whether a study drug works, how it works, and whether it is safe to prescribe to patients.

This summary reports the results of only one study. The results of this study might be different from the results of other studies that the researchers look at.


More information can be found in the scientific
abstract of this study, which you can access here:
View ESMO Scientific Abstract

What did this study look at?

  • Advanced breast cancer is cancer that has spread either within or beyond the breast.
  • Some people have a type of advanced breast cancer that is sensitive to chemical messengers in the body (hormones) such as estrogen.
    • This cancer is called hormone receptor positive (HR+)/human epidermal growth factor receptor 2 negative (HER2−) advanced breast cancer.
  • Palbociclib is a type of medicine known as a CDK4/6 inhibitor. It works by blocking a group of proteins that cancer cells need for growth.
    • This may help to slow down the growth of the cancer.
  • Palbociclib is approved to treat HR+/HER2− advanced breast cancer in combination with drugs called aromatase inhibitors (AIs for short). An example of an AI is letrozole.
  • AI treatment lowers the amount of estrogen that the body produces.
    • Estrogen can help breast cancer cells to grow. Lowering the amount of estrogen with AIs can slow or stop tumor growth.
  • This study looked at women with advanced breast cancer who took palbociclib + AI as their first treatment for breast cancer. This was a ‘real-world’ study, not a clinical trial.
    • In clinical trials, the treatments people receive are often tightly controlled so that the effect of a new medicine can be tested.
    • In real-world studies, people receive approved medicine in a routine clinical setting. This type of study helps researchers understand how medicines are used in clinical practice and whether the results seen in real life are similar to those seen in clinical trials. It also provides information on people who may not be eligible for clinical trials, presenting a more realistic real-world view.
  • This summary describes:
    • the women’s characteristics, and
    • how long they lived without their cancer getting worse while taking palbociclib + an AI.

Who took part in this study?

  • Researchers identified women with HR+/HER2− advanced breast cancer from a US medical database. This database has information on 2 million people from 275 cancer clinics.

What were the results of the study?

More results from this study can be found here:
View ESMO Scientific Abstract

What were the main conclusions reported by the researchers?

  • The results of this real-world study support the findings of previous clinical studies of palbociclib-based therapy.
  • The results suggest that palbociclib + an AI is an appropriate first treatment for women with HR+/HER2− advanced breast cancer in routine clinical practice in the US.

Who sponsored this study?

Pfizer Inc.
235 East 42nd Street NY,
NY 10017
Phone (United States): +1 212-733-2323

Pfizer would like to thank all of the women who took part in this study.

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