Pfizer's Palbociclib Slows Tumor Growth in Breast Cancer Patients

Pfizer's new drug palbociclib slows tumor growth in breast cancer patients, the drugmaker announced Sunday.

A phase 2 clinical trial was conducted on 165 women with advanced ER positive, HER2 negative breast cancers. Participants were either given letrozole plus palbociclib or letrozole only.

Researchers found that women on palbociclib plus hormone drug letrozole lived for some 20.2 months before the cancer advanced compared with women in the control group who had a progression-free survival period of 10.4 months, Reuters reported.

"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, according to a statement released by the company.

The U.S. Food and Drug Administration (FDA) has already given Palbociclib a Breakthrough Therapy designation April 2013. The results of the Phase 2 study are expected to boost the approval process of the drug.

If approved, Palbociclib could make over $5 billion in annual sales, Reuters reported.

Palbociclib is aimed at treating breast cancer patients with hormone-receptor-positive cancer. Estrogen receptor positive cancer cells need the hormone estrogen to grow. The cancer is usually treated by blocking the release of estrogen.  

According to Bloomberg, Pfizer's drug is the first drugs in ten years that has shown some promise in treating this common type (ER positive) of breast cancer. Palbociclib is an inhibitor of cyclin-dependent kinases (CDKs) 4 and 6. The drug works by preventing the tumor from growing and spreading.

"These are as impressive results as I have ever seen. I do not say that lightly." said Dennis Slamon, a UCLA physician scientist,according to Forbes. Slamon has worked with Pfizer to develop palbociclib and owns Pfizer stock.

The study results could push Pfizer get an accelerated approval for its drug, Forbes reported. The drug developer's rivals also have breast cancer drugs in the pipeline. Eli Lilly recently presented results of clinical trials involving its drug bemaciclib, which is an inhibitor of CDK4/6. Novartis, too, has a similar drug in the final phases.