Pfizer Inc. says that an experimental breast cancer drug it is developing was more effective than an older therapy at slowing the progression of advanced breast cancer.

The experimental treatment is designated PD-0332991. Pfizer says patients who took PD-0332991 and an older drug, letrozole, had progression-free survival of 26.1 months on average.

That means they lived about two years and two months before they died from their cancer or their disease began to progress again. Patients who were treated with letrozole alone had progression-free survival of 7.5 months on average.

Patients in the mid-stage trial had gone through menopause. They were all diagnosed with hormone receptor positive breast cancer lacking the protein HER2. Pfizer says about 60 percent of breast cancers fit that description. The company plans to start a late-stage trial of PD-0332991 and letrozole in post-menopausal women in 2013.

Pfizer will report more data from the study at a future medical conference. The New York drugmaker is also testing PD-0332991 as a treatment for other types of cancer.

Letrozole is a pill sold by Novartis AG under the brand name Femara. Generic versions are also available.

Release Date: December 5, 2012
Source: The Associated Press