Pfizer’s Palbociclib Meets Endpoint in Phase 2 Breast Cancer Trial

Andrew Klips  |

Amid a swath of carnage on Wall Street on Monday with the Dow Jones Industrial Average collapsing more than 300 points as the day heads towards a close, shares of Pfizer, Inc. (PFE) are holding in the green after news that a mid-stage trial for breast cancer patients demonstrated encouraging results.

Pfizer said that the Phase 2 PALOMA-1 trial of its drug candidate called palbociclib combined with the widely-used drug letrozole hit its primary endpoint by demonstrating a “statistically significant and clinically meaningful” improvement in progression-free survival as compared to letrozole alone. The trial enrolled post-menopausal women with ER+ (estrogen receptor positive) and HER2- (human epidermal growth factor receptor 2 negative) breast cancer that was either local or had recently spread to other parts of the body. PALOMA-1 is being conducted at 101 clinical sites worldwide.

The specific indication Pfizer is targeting affects about 60 percent of all advanced breast cancer patients, giving it blockbuster potential. The American Cancer Society estimates that about 232,670 new cases of breast cancer will be diagnosed in 2014 and that approximately 40,000 women will die from the disease.

“We are delighted with the final data, which suggest the potential for palbociclib to transform the standard of care for post-menopausal women with ER+ and HER2- advanced breast cancer,” said Dr. Mace Rothenberg, senior vice president of Clinical Development and Medical Affairs and chief medical officer for Pfizer Oncology, in a statement on Monday.

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Palbociclib is one of less than two dozen drugs that has been designated a “Breakthrough Therapy” by the FDA since the new fast-track designation was first introduced late in 2012. Breakthrough Therapies must meet areas of great unmet medical need and can potentially maneuver more quickly down the regulatory pathway to commercialization. The FDA awarded Palbociclib the distinction in April based upon interim data from the PALOMA-1 trial.

Palbociclib is a first-in-class oral drug candidate that selectively blocks specific enzymes, called cyclin-dependent kinsases (CDKs) 4 and 6. These enzymes are overactivated in several types of cancer, promoting tumor growth and spreading. Research shows that inhibiting CDK 4 and 6 can stop growth of certain cell lines at an early stage.

When Pfizer released its initial trial findings in December 2012, the interim data showed that women taking the drug lived an average of 26.1 months before their tumors got worse, besting the average of only 7.5 months for patients receiving letrozole by itself. Letrozole, a drug that blocks estrogen production, is better known by its brand name Femara, a drug marketed by Novartis AG (NVS) .

The side effects of palbociclib in the latest batch of data were consistent with information previously reported. Pfizer is already enrolling patients in PALOMA-2, a Phase 3 trial, but said that it plans to discuss the results of PALOMA-1 with the FDA and other regulatory agencies to determine the next steps. It is presumable that Pfizer, who is in need of a new blockbuster seller since losing patent protection for mega-drugs like Viagra and Lipitor in recent years, is aiming to meet with these agencies to delineate the fastest path to commercialization.

Shares of PFE have slipped from intraday highs, but are still ahead by about 1 percent at $30.92. 

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