Pfizer announced results from the Phase 2 PALOMA-1 study that is investigating the use of palbociclib (PD-0332991) in combination with letrozole in patients with advanced breast cancer. Palbociclib is an oral and selective inhibitor of cyclin dependent kinases (CDK) 4 and 6 for the potential treatment of patients with breast cancer.

RELATED: Breast Cancer Resource Center

PALOMA-1 (also known as Study 1003 and TRIO-18) is designed to assess progression-free survival (PFS) in post-menopausal women with estrogen receptor positive (ER+), human epidermal growth factor receptor 2 negative (HER2-) locally advanced or metastatic breast cancer receiving palbociclib 125mg once daily (for three out of four weeks in repeated cycles) in combination with letrozole vs. letrozole alone (2.5mg once daily on a continuous regimen). Part 1 of the trial enrolled 66 patients with ER+, HER2- advanced breast cancer while Part 2 enrolled 99 additional patients whose tumors were selected for presence of biomarkers: cyclin D1 amplification and/or p16 loss.

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PALOMA-1 achieved its primary endpoint by significantly prolonging progression-free survival (PFS) compared with letrozole alone in post-menopausal women with ER+, HER2- locally advanced or metastatic breast cancer. In women treated with 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). 

Palbociclib was granted Breakthrough Therapy designation from the FDA in April 2013, for the initial treatment of women with advanced or metastatic ER+, HER2- breast cancer. Two Phase 3 studies (PALOMA-2 and PALOMA-3) have been initiated to study palbociclib in advanced/metastatic breast cancer.

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This article originally appeared on MPR