Pfizer’s novel CDK 4/6 inhibitor palbociclib plus letrozole significantly prolonged progression-free survival in patients with advanced breast cancer

Pfizer Inc. today announced detailed results from the PALOMA-1 study, a randomized Phase 2 study of palbociclib (PD-0332991) in combination with letrozole. PALOMA-1 achieved its primary endpoint by significantly prolonging progression-free survival (PFS) compared with letrozole alone in post-menopausal women with estrogen receptor positive (ER+), human epidermal growth factor receptor 2 negative (HER2-) locally advanced or metastatic breast cancer. For women treated with the combination of palbociclib plus letrozole, the median PFS was 20.2 months, a statistically significant improvement compared to the 10.2 months of PFS in women who received letrozole alone (HR=0.488 [95% CI: 0.319, 0.748]; p=0.0004). These data will be presented today by Dr. Richard S. Finn, associate professor of medicine at University of California, Los Angeles (UCLA) at the American Association of Cancer Research (AACR) Annual Meeting 2014 in San Diego (Abstract #CT101).

“These data demonstrate the potential of palbociclib to be a major advance in the treatment of women with this type of advanced breast cancer,” said Dr. Mace Rothenberg, senior vice president of Clinical Development and Medical Affairs and chief medical officer for Pfizer Oncology. “We are proud to be at the forefront of research and development with respect to this promising new class of investigational anticancer agents and have initiated a broad clinical development program for palbociclib that includes breast and non-breast cancers.”

Final results for the secondary efficacy endpoints of duration of treatment and clinical benefit rate demonstrated superiority in the palbociclib plus letrozole arm compared to the letrozole-only arm. Per the PALOMA-1 trial protocol, an initial assessment of overall survival (OS), a secondary endpoint, was also performed. Based on the events at the time of the assessment, a median OS of 37.5 months was observed in the combination arm versus 33.3 months for those who received letrozole alone, a difference of 4.2 months (HR = 0.813, 95% CI: 0.492, 1.345). This OS observation at the time of final PFS analysis was not statistically significant. A follow-up OS analysis will be conducted following the accrual of additional events.

The combination of palbociclib and letrozole was generally well-tolerated and the safety profile of the combination was consistent with previously reported data. The most common adverse events in the palbociclib plus letrozole arm were neutropenia (a decrease of the neutrophil count), leukopenia (a decrease in the total white blood cell count), fatigue and anemia. The neutropenia observed with the combination in this study was non-cumulative and clinically manageable. No cases of febrile neutropenia were reported in either arm of the study. Neutropenia is an on-target, anti-proliferative side effect of palbociclib and signifies inhibition of CDK4 and its effect on bone marrow.

Palbociclib received Breakthrough Therapy designation from the United States Food and Drug Administration (FDA) in April 2013, for the initial treatment of women with advanced or metastatic ER+, HER2- breast cancer. This designation was based on interim data from the PALOMA-1 trial. Pfizer continues to work with the FDA and other regulatory authorities to define the appropriate regulatory path forward for palbociclib.

Pfizer invites investors and the general public to view and listen to a webcast of a presentation by Pfizer’s Oncology leadership today at 1:30 p.m. Pacific Daylight Time, in connection with the presentation of the final results of PALOMA-1. To view and listen to the webcast, visit our website at www.pfizer.com and click on the “Review of Palbociclib Phase 2 PALOMA-1 Results at AACR Annual Meeting 2014” webcast link in the For Investors section located on the lower right-hand corner of that page.