Adding a new drug called Ibrance (palbociclib) to standard hormone therapy helped keep a common type of breast cancer under control measurably longer than the hormone therapy alone, a new study shows.
"Palbociclib stops cancer cells from growing," said study author Dr. Nicholas Turner, team leader at the Institute of Cancer Research in London, England.
Adding the drug was so effective that the trial was stopped early so that those who were in the "control" group (taking an inactive placebo) could also be offered the drug.
The findings are to be published online in the New England Journal of Medicine, to coincide with a planned presentation Saturday at the American Society of Clinical Oncology annual meeting in Chicago. Pfizer, the drug's maker, helped fund the study.
Turner's team randomly assigned 521 women to get either Ibrance plus the standard hormone therapy known as fulvestrant, or fulvestrant with a placebo pill.
All of the study participants had advanced breast cancer, a type known as hormone receptor-positive and HER2-negative. Cancers that are hormone receptor-positive are fueled by estrogen or progesterone. Those that are HER2-negative do not have the growth-promoting hormone HER2.
All of the women had cancers that had spread ("metastatic" disease), and then worsened or relapsed after they had taken initial hormone therapy. The median age of the patients was about 57.
The researchers measured the average time it took for disease to progress to evaluate how well the new drug worked to control the cancer. The average time in the Ibrance/fulvestrant group was 9.2 months, compared to 3.8 months in the fulvestrant-alone group, the investigators found.
The new drug targets two key proteins that fuel the growth of this type of cancer, Turner said. Fulvestrant is a commonly used hormone therapy.
About 75 percent of all breast cancers are hormone receptor-positive, HER2-negative, according to Turner.
Patients on the combo treatment had a small increase in fatigue, hair thinning and mouth soreness compared to the solo-therapy group, Turner said. They were also more likely to get infections. Only a few women dropped out due to side effects.
A longer follow-up is needed to see the effect of the drug on the women's overall survival, not just keeping the cancer under control, Turner said. The researchers are also studying the possibility of using the drug in women with early stage hormone receptor-positive breast cancer.
Dr. Joanne Mortimer, director of Women's Cancer Programs at the City of Hope Cancer Center, in Duarte, Calif., called the study results impressive.
"Keeping your cancer under control for an additional five months is an important result," she said.
The U.S. Food and Drug Administration granted Ibrance accelerated approval earlier this year for use in combination with the drug letrozole for women with advanced estrogen receptor-positive, HER2-negative breast cancer who had not yet gotten hormone therapy for their metastatic disease.
So, doctors could use Ibrance "off label," Mortimer said. However, not all insurers may pay for it, she added. The drug is expensive, about $10,000 a month.
"Once this study is presented, most insurers will probably cover it," Mortimer said.