Pfizer Inc., of New York, said the randomized Phase II (PALOMA-1) of palbociclib achieved its primary endpoint by demonstrating a statistically significant and clinically meaningful improvement in progression-free survival for the combination of palbociclib and letrozole compared to letrozole alone in postmenopausal women with estrogen receptor-positive, human epidermal growth factor receptor 2-negative locally advanced or newly diagnosed metastatic breast cancer.