A Comprehensive Literature Review of Available Real-World Evidence Evaluating CDK4/6 Inhibitors in Patients with HR-Positive, HER2-Negative Advanced/Metastatic Breast Cancer

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Cyclin-dependent kinase (CDK)4/6 inhibitors have been approved for treating hormone receptor (HR)-positive HER2-negative advanced/metastatic breast cancer and are considered standard of care for treatment. Harbeck and colleagues assessed and qualitatively reviewed the available real-world evidence (RWE) that had been published on their efficacy. They conducted a thorough systematic literature review to characterize RWE studies published between 2015 and 2019 evaluating CDK4/6 inhibitor use in patients with HR-positive/HER2-negative advanced/metastatic breast cancer. This is important because often randomized controlled trials do not evaluate end points such as quality of life and economic outcomes and insights into subpopulations including patients with poor performance status and patients with brain metastases as well as elderly patients. RWE offers valuable insight into the efficacy of treatment for these populations. A published systematic review focused on RWE investigations of CDK4/6 inhibitors in the treatment of HR-positive/HER2-negative advanced/metastatic breast cancer has not been previously conducted. Therefore, a comprehensive systematic literature review on this topic was the goal of this investigation.

The Ovid platform was used to search MEDLINE (including Epub ahead of print and in-process, and other non-indexed citations), Embase, as well as a range of Evidence-Based Medicine Reviews databases.

For prespecified conferences, including the American Society of Clinical Oncology, the European Society for Medical Oncology (ESMO), ESMO Breast Cancer, ESMO Asia, and the San Antonio Breast Cancer Symposium, grey literature searches were conducted to find posters and abstracts presented between January 2015 and December 2019. To validate the findings from the database and grey literature searches, the investigators searched ClinicalTrials.gov and the bibliographies of relevant published reviews.

The literature searches yielded 1980 records, of which a total of 114 studies were identified as appropriate to include in the systematic review, of which 85 were scientific conference presentations only.

Improved outcomes were demonstrated, through most real-world studies investigating palbociclib. Long-term and comparative data between CDK4/6 inhibitors and endocrine monotherapy, and within the CDK4/6 inhibitor class were limited.

CDK4/6 inhibitors were associated with improved outcomes in HR-positive/HER2-negative advanced/metastatic breast cancer, as evidenced through available RWE studies; however, it is needed for studies to be conducted with longer duration of follow-up periods. In addition, in the future a focus on studies of longer follow-up is required to compare both between CDK4/6 inhibitors and endocrine monotherapy, and within the CDK4/6 inhibitor class.


Harbeck N, Bartlett M, Spurden D, et al. CDK4/6 inhibitors in HR+/HER2- advanced/metastatic breast cancer: a systematic literature review of real-world evidence studies. Future Oncol. 2021;17:2107-2122.

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