Pfizer's Ibrance drug slows progression of breast cancer

By Deena Beasley

CHICAGO May 30 (Reuters) - A Phase III trial of Pfizer Inc (NYSE: PFE - news) 's drug Ibrance showed that, in combination with hormone therapy, the drug more than doubled the duration of disease control for women with the most common type of breast cancer.

At the time of an interim analysis, patients given Ibrance in combination with AstraZeneca Plc (NYSE: AZN - news) 's Faslodex (fulvestrant), a widely used treatment to block estrogen, lived an average of 9.2 months before their cancer worsened. This compared with 3.8 months for patients treated with Faslodex and a placebo.

The trial enrolled 521 patients whose breast cancer was classified as estrogen-receptor positive, human epidermal growth factor receptor 2-negative (ER+/HER2-). This category accounts for about 75 percent of all breast cancers.

Ibrance, or palbociclib, was given conditional approval by the U.S. Food and Drug Administration in February for such patients, but only those who had not previously been treated for advanced breast cancer.

Ibrance works by blocking two enzymes, cyclin-dependent kinase 4 and 6, that are involved in cell growth. Some Wall Street analysts have predicted the drug could eventually generate annual sales of more than $5 billion.

Pfizer announced in April that the pivotal trial was stopped early after meeting its goal of demonstrating that Ibrance delayed disease progression. Overall survival results are not yet available, said Dr. Nicholas Turner, a consultant medical oncologist at The Royal Marsden and a team leader at The Institute of Cancer Research in London, and the study's lead author.

The most common adverse side effects seen in the trial involved blood count irregularities, with 2.6 percent of Ibrance patients stopping treatment due to side effects.

Pfizer is currently conducting a study of Ibrance in women with advanced breast cancer not previously treated with hormone therapy.

(Reporting By Deena Beasley; Editing by Diane Craft)