Yesterday Pfizer (PFE) won FDA approval for its breast cancer drug known as palbociclib, which was approved to treat patients with a very specific form of advanced breast cancer. The drug, which will be marketed as Ibrance, is expected to be a potential blockbuster drug for the company. At the intended monthly price of $9,850, Ibrance is expected to make the company $4 billion by 2020. 

The approval, though anticipated, was not expected for another two months or so. The drug is in the Accelerated Approval program, by which drug companies are given early approval for drugs that treat an unmet medical need and treat serious medical conditions. Even with early approval these companies still have to run a confirmatory phase 4 trial to confirm previous findings; if the drug doesn't show efficacy in these phase 4 trials then the FDA has a rule in place where they can pull the drug from the market. 

According to the FDA announcement,

The drug’s efficacy was demonstrated in 165 postmenopausal women with ER-positive, HER2-negative advanced breast cancer who had not received previous treatment for advanced disease. Clinical study participants were randomly assigned to receive Ibrance in combination with letrozole or letrozole alone. Participants treated with Ibrance plus letrozole lived about 20.2 months without their disease progressing (progression-free survival), compared to about 10.2 months seen in participants receiving only letrozole. Information on overall survival is not available at this time.

Ibrance itself is an oral pill that inhibits cyclin-dependent kinases (CDKs) 4 and 6. It is believed that by inhibiting CDks 4 and 6, cellular progression of the patients' advanced breast cancer will be inhibited. The efficacy of Ibrance was seen in the PALOMA-1 trial where it met the primary endpoint of the trial, Progression-Free Survival (PFS).  The trial compared a combination of Ibrance and letrozole (current standard of care for advanced breast cancer patients) against letrozole alone. Ibrance met the primary endpoint of the trial and was superior to letrazole alone.

We believe that Pfizer is back on track with this drug and that it desperately needed a new blockbuster drug in the pipeline after many years of patent expirations of other drug compounds.