Pfizer Inc's experimental drug against breast cancer nearly doubled the amount of time patients lived without their cancer getting worse, as showed the clinical trial, researchers said.

The Phase 2 study, which involved women with the most common form of breast cancer, found that those treated with hormone drug letrozole plus Pfizer's palbociclib lived for an average of 20.2 months before their cancer progressed, compared with 10.2 months for patients given letrozole alone, reports Newsmax Health.

The trial tested the pill, which targets proteins involved in cell division, in post-menopausal women with locally advanced or newly diagnosed breast cancer that had spread to other parts of the body.

Side effects seen in the trial, including low blood cell counts and fatigue, were manageable, Dr. Richard Finn, associate professor of medicine at the University of California, Los Angeles, and a lead author of the study said in a telephone interview ahead of the study's presentation on Sunday in San Diego at a meeting of the American Association for Cancer Research.