Pfizer’s novel breast cancer drug shows promise

Pfizer’s new breast cancer drug palbociclib (PD-0332991) has shown promise in phase II trials, but has not yet proved that it can extend the lives of patients.

The drug has been given Breakthrough Therapy designation by the FDA, and has been tipped as a potential blockbuster for Pfizer, with analysts predicting sales of up to $10 billion.

A phase II study of the drug, PALOMA-1, showed the drug can significantly prolong progression-free survival (PFS) when combined with standard treatment letrozole, compared to patients taking letrozole alone.

The study was presented at the American Association for Cancer Research (AACR) Annual Meeting 2014 being held in San Diego, where a number of important new studies are being presented.

The study was in post-menopausal women with estrogen receptor positive (ER+), non-HER2 locally advanced or metastatic breast cancer, and showed those taking the new combination had an average progression free survival of 20.2 months, a very significant improvement on the 10.2 months in those who received letrozole alone.

However the drug failed to hit its secondary endpoint, overall survival (OS): a median OS of 37.5 months was observed in the combination arm versus 33.3 months for those who received letrozole alone, a difference of 4.2 months. This OS observation was not statistically significant, but Pfizer says a follow-up OS analysis will be conducted following the accrual of additional events.

CDK 4/6 inhibitors

Pfizer’s drug is the first in a new class of drugs, the CDK 4/6 inhibitors. However the company doesn’t have the field to itself – both Lilly and Novartis have contenders in the pipeline as well.

Lilly will also be presenting its candidate LY2835219 at the AACR meeting, while Novartis’ drug LEE011 is now in phase I, with some commentators suggesting it could be a best-in-class performer.

Pfizer’s palbociclib has been designated a Breakthrough Therapy, but because the new approval route has not been in operation for long, it is unclear whether Pfizer will be permitted to file for approval with the phase II data, or whether the FDA will require more robust data before it accepts an application. Pfizer says it is in discussion with the regulator on these issues, and a decision on the next steps is expected later this year.


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