Pfizer Inc.'s Ibrance in combination with letrozole showed improved progression-free survival in a phase 3 study for treating breast cancer.

Ibrance, in combination with an aromatase inhibitor, is approved in the U.S. as an initial endocrine-based therapy in postmenopausal women with hormone receptor-positive, human epidermal growth factor receptor 2-negative, or HER2-, advanced or metastatic breast cancer.

The U.S. Food and Drug Administration had granted regular approval for the indication in March based on data from the Paloma-2 phase 3 trial in which the combination achieved progression-free survival of 24.8 months versus14.5 months for placebo plus letrozole.

The latest data from the trial showed that the drug combination improved median progression-free survival by more than one year to 27.6 months compared to 14.5 months for placebo and letrozole.

The treatment reduced the risk of disease progression by 44%, with clinical benefit observed across all patient subgroups receiving the combination.

"The updated findings from Paloma-2 provide additional evidence to support the use of palbociclib with an aromatase inhibitor as a standard of care in the first-line setting for postmenopausal patients with hormone receptor-positive, HER2- metastatic breast cancer across all patient subgroups," Hope Rugo, lead author of the study, said in a news release.

Ibrance was the first CDK 4/6 inhibitor approved by any regulatory authority and now is approved in more than 75 countries.