By Amy Norton
WEDNESDAY, Nov. 16, 2016 (HealthDay News) -- A recently approved drug can help slow the progression of advanced breast cancer, a new clinical trial confirms.
The drug, called palbociclib (Ibrance), was approved in the United States last year for treating advanced cases of ER-positive breast cancer. That means the cancer uses the hormone estrogen to help fuel its growth.
The approval was based on an earlier-stage study where the drug, used along with a standard drug called letrozole (Femara), helped keep women's cancer at bay. Palbociclib doubled the time patients remained progression-free compared to letrozole alone.
The new findings, published in the Nov. 17 New England Journal of Medicine, confirm the earlier results in a larger group of women.
"We found that the degree of clinical benefit was, again, remarkable," said lead researcher Dr. Richard Finn, an assistant professor of medicine at the University of California, Los Angeles.
Among postmenopausal patients in the trial, those given the drug combination typically remained progression-free for just over two years. That compared to just over 14 months among women treated with letrozole alone.
"This is an incredibly important step" in improving the outlook for women with advanced breast cancer, said Dr. Antonio Wolff, a professor of oncology at Johns Hopkins University in Baltimore.
"We know this isn't the final answer," added Wolff, who wrote an editorial published with the study. Other drugs aimed at stalling advanced breast tumors are in development, he noted.
But palbociclib should be considered "a new standard" for treating advanced ER-positive breast cancer, Wolff said.
Palbociclib is the first in a new class of drugs designed to inhibit two enzymes called CDK4 and CDK6, which help ER-positive breast tumors spread. Palbociclib is a capsule taken once a day for three weeks, followed by one week off.
Letrozole, meanwhile, works by lowering estrogen levels in the body.
About two-thirds of breast cancers have receptors for estrogen and/or the hormone progesterone, according to the American Cancer Society.
In this latest trial, Finn's team tested palbociclib/letrozole as a first-line treatment for advanced cancer that had spread beyond the breast. They randomly assigned 666 women to receive the drug duo or letrozole alone, and followed them for up to three years.
At that point, 44 percent of women in the palbociclib group had either died or seen their cancer progress. That compared with 62 percent of women on letrozole alone, according to the study.