Short-term pre-operative treatment with palbociclib significantly reduced Ki67, a marker of cancer cell proliferation, in treatment-naïve patients with early-stage breast cancer, according to data presented at the American Academy for Cancer Research (AACR) Annual Meeting 2016.1

“The use of targeted therapies has been increasing in the last few years. It is crucial to determine that these drugs do hold activity against tumor cells,” said lead author, Monica Arnedos, MD, an assistant professor at Gustave Roussy Cancer Campus in Villejuif, France. “In the case of palbociclib, no predictive biomarkers have been identified to date, and there are still no data about its potential efficacy in the early setting.”

For the phase 2 trial, researchers sought to investigate if short-term preoperative palbociclib treatment is associated with decreased proliferation and early biomarker changes in patients with early breast cancer. Investigators enrolled 100 patients and randomly assigned them 3:1 to receive palbociclib 125 mg orally daily for 14 days until the day before surgery or no treatment. Immunostaining, FISH, and gene expression arrays were performed pre- and post-treatment.

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Results showed 58% of patients who received palbociclib treatment had an antiproliferative response in their tumors vs 10% of patients who received no treatment. Among the 93% of patients with hormone receptor (HR)-positive, human epidermal growth factor receptor 2 (HER2)-negative patients, 72% demonstrated decreased protein Ki67 as compared with 5% in the control arm. Patients with HER2-positive tumors or those with triple-negative breast cancer exhibited no Ki67 response.

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“Palbociclib works in untreated early-stage breast cancer, and the magnitude of this activity was higher than expected,” Dr Arnedos said.

However, the authors note that further research is needed to confirm the findings of this study. Future studies should also include more patients with HR-negative breast cancer.

Palbociclib is a cyclin-dependent kinase 4 and 6 inhibitor. It was approved in February 2015 by the U.S. Food and Drug Administration (FDA) in combination with letrozole for the treatment of postmenopausal women with estrogen receptor-positive, HER2-negative advanced breast cancer as initial endocrine-based therapy for metastatic disease.


  1. Arnedos M, Cheaib B, Bayar MA, et al. Anti-proliferative response and predictive biomarkers to palbociclib in early breast cancer. The Preoperative Palbociclib (POP) randomized trial. Oral presentation at: AACR Annual Meeting 2016; April 16-20, 2016; New Orleans, LA.