Pfizer announced that the Phase 2 PALOMA-1 trial met its primary endpoint by achieving a statistically significant and clinically meaningful improvement in progression-free survival (PFS) for the combination of palbociclib and letrozole (Femara; Novartis) vs. letrozole alone in postmenopausal women with estrogen receptor positive (ER+), human epidermal growth factor receptor 2 negative (HER2-) locally advanced or newly diagnosed metastatic breast cancer.

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Palbociclib is an investigational oral targeted agent that selectively inhibits cyclin-dependent kinases (CDKs) 4 and 6 to regain cell cycle control and block tumor cell proliferation.

PALOMA-1 is a Phase 2 study assessing the PFS of palbociclib (125mg once daily for 3 out of 4 weeks in repeated cycles) in combination with letrozole vs. letrozole alone (2.5mg once daily on a continuous regimen) in postmenopausal women with ER+, HER2- advanced breast cancer. PFS is defined as time from randomization to time of disease progression or death from any cause.

In April 2013, palbociclib received Breakthrough Therapy Designation by the FDA for the initial treatment of women with advanced or metastatic ER+, HER2- breast cancer based on data from the PALOMA-1 trial. A randomized Phase 3 trial (PALOMA-2) in this patient population is currently in enrollment.

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