Efficacy of Palbociclib Plus Letrozole in Treatment of HER-Positive, HER2-Negative Metastatic Breast Cancer


A study evaluated the real-world benefit of palbociclib plus endocrine therapy as a first-line treatment in HR-positive, HER2-negative metastatic breast cancer to correlate the efficacy of the combination with neutropenia.

Researchers found that the efficacy of palbociclib plus letrozole in the treatment of hormone receptor (HR)-positive, human epidermal growth factor receptor 2 (HER2)-negative metastatic breast cancer in the real-world setting was similar to the results from the PALOMA-2 trial.1 In addition, patients with a higher absolute neutrophil count (ANC) were found to have a higher risk for early disease progression.1

The research was presented at the 2019 San Antonio Breast Cancer Symposium in San Antonio, Texas.

The ANC is the real number of white blood cells that are neutrophils, which help the body fight infection. Typically, having an ANC below 500 means there is a high risk of contracting an infection.2

The combination of a cyclin-dependent kinase 4/6 (CDK4/6) inhibitor plus endocrine therapy has been shown to significantly improve the progression free survival (PFS) in patients with HR-positive, HER2-negative metastatic breast cancer. The study was conducted to evaluate the real-world benefit of palbociclib plus endocrine therapy as the first line treatment in HR-positive, HER2-negative metastatic breast cancer to correlate efficacy of the combination with neutropenia.1

Participants were treated with palbociclib plus an endocrine therapy between January 1, 2015, and March 1, 2018, at Moffitt Cancer Center in Tampa, Florida. Using the Kaplan-Meier analysis, the PFS was determined and the predictive value of ANC and neutrophil-to-lymphocyte ratio (NLR) for PFS were examined using univariable and multivariable Cox models.1

Out of 165 patients in the study, the median PFS was 24.19 months. For patients with bone metastasis only, the median PFS was not reached and for patients with non-bone-only metastasis, the median PFS was also 24.19 months.1

Patients with a higher ANC are at high risk of early disease progression according to the researchers, but they did not find a significant association between the value of NLR and the risk of disease progression.1


  • Real-world benefit of CDK4/6 inhibitor and endocrine therapy combination in metastatic breast cancer and correlation with neutropenia. Accessed Dec 2, 2019. https://plan.core-apps.com/sabcs2019/abstract/c384ee17f029c6ed91aef896ddbba228
  • NCI Dictionary of Cancer Terms: Absolute Neutrophil Count. Accessed Dec 3, 2019. https://www.cancer.gov/publications/dictionaries/cancer-terms/def/absolute-neutrophil-count.

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