May 16 (Reuters) - Pfizer Inc, which is in the process of trying to acquire British rival AstraZeneca for more than $100 billion, on Friday said it planned to seek U.S. approval for palbociclib, its experimental drug for advanced breast cancer, in the third quarter.
The largest U.S. drugmaker said it made the decision to submit its application to the Food and Drug Administration following discussions with the regulatory agency about the results of a midstage clinical trial.
Palbociclib had received the FDA's new breakthrough designation given to help speed up the approval process for potentially important new medicines.
Pfizer presented data from the trial at a cancer meeting last month. Patients in the study who took the experimental Pfizer medicine plus the hormone drug letrozole went 20.2 months on average before their cancer began to worsen, compared with 10.2 months for those that received only letrozole.
Palbociclib is considered to be one of the most important medicines in Pfizer's developmental pipeline. A rival drug is also being developed by Eli Lilly and Co, which several analysts have said appears promising.
Pfizer shares were up 1.2 percent at $29.41 in early afternoon trading on the New York Stock Exchange. (Reporting by Bill Berkrot, editing by G Crosse)