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Promising Drug Doubled Positive Effect in Hormone-Receptor Positive Breast Cancer
Posted Date: 4/6/2014 7:30 AM


  • Palbociclib is a drug developed to fight ER+ breast cancer cells
  • In early studies the drug when used in combination showed a significant increase in progression-free survival
  • Palbociclib was given Breakthrough Therapy designation by the FDA earlier this year
  • Final study results validate earlier findings and could lead to greatly improved outcomes for breast cancer patients

Breast cancer researchers from the Revlon/UCLA Women’s Cancer Research Program at UCLA’s Jonsson Comprehensive Cancer Center (JCCC) announced final clinical trial results this morning that showed the amount of time patients were on treatment without their cancer worsening (called progression-free survival) was effectively doubled in women with advanced breast cancer who took the experimental drug palbociclib.

The results of the phase 2 clinical trial were announced at the American Association for Cancer Research AACR Annual Meeting 2014 in San Diego.

Palbociclib (PD 0332991) is an investigational drug discovered and being developed by Pfizer, Inc. The preclinical work testing palbociclib in a panel of human breast cancer cells growing in culture dishes showed very encouraging activity, specifically against estrogen-receptor-positive (ER+) cancer cells.

This led to a clinical study collaboration with Pfizer, led by Dr. Richard S. Finn, associate professor of medicine at JCCC. The phase 1 study built on laboratory work from the Translational Oncology Research Laboratory directed by Dr. Dennis Slamon, professor of medicine at JCCC and director of the Revlon/UCLA Women’s Cancer Research Program.

Dr. Dennis Slamon Dr. Richard Finn
Dr. Dennis Slamon Dr. Richard Finn

The preclinical observations were moved into a phase 1 clinical study led by Finn and Slamon at UCLA. The study was designed to determine the doses and initial safety results of a combination with letrozole, a commonly used drug for ER+ advanced breast cancer. Once the phase 1 study was completed, the phase 2 study was performed in 165 post-menopausal breast cancer patients with advanced ER+, HER2- disease.

“By combining the test drug, palbociclib, with the standard drug letrozole, we demonstrated a dramatic and clinically meaningful effect on progression-free survival in women with ER+ advanced breast cancer,” Finn said. “We are gratified and excited that these results confirm the preclinical work we began at the Translational Lab.”

As the primary endpoint of the study, progression-free survival was 20.2 months for patients who received palbociclib plus letrozole and 10.2 months for those who received letrozole only. The PFS results indicated a 51 percent reduction in the risk of disease progression with the addition of palbociclib to letrozole.

“Our final results very much validate the Translational Laboratory approach,” said Slamon. “By identifying the effective treatment targets in the correct patients, we advance personalized cancer treatment that we hope will greatly improve outcomes for this group of women with breast cancer. These results are as exciting as the initial results we saw for trastuzumab (Herceptin) in HER2+ breast cancers, but represent a new approach for women with ER+ advanced breast cancer. This group is different from HER2+ breast cancer and affects approximately 60 percent of all advanced breast cancer patients compared with approximately 20 percent for HER2.”

This Phase 2 clinical study was sponsored by Pfizer.

UCLA's Jonsson Comprehensive Cancer Center has more than 240 researchers and clinicians engaged in disease research, prevention, detection, control, treatment and education. One of the nation's largest comprehensive cancer centers, the Jonsson center is dedicated to promoting research and translating basic science into leading-edge clinical studies. In July 2013, the Jonsson Cancer Center was named among the top 12 cancer centers nationwide by U.S. News & World Report, a ranking it has held for 14 consecutive years. For more information on the Jonsson Cancer Center, visit our website at


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