New Targeted Drug Slows Growth and Spread of Metastatic Breast Cancer

ASCO Annual Meeting
May 30, 2015

A large phase III study has found that a new targeted therapy, called palbociclib (Ibrance), delayed the growth and spread of advanced hormone receptor-positive breast cancer by roughly five months when combined with the standard hormonal therapy fulvestrant (Faslodex). This combination could become a new treatment option for women with hormone receptor-positive, HER2-negative breast cancer that has spread to other parts of the body.

Palbociclib is a new drug that is given as a pill to swallow. It targets specific proteins, called cyclin dependent kinases (CDKs) 4 and 6, that contribute to breast cancer’s growth and survival. This type of treatment blocks the growth and spread of cancer cells while limiting damage to healthy cells.

For this study, 521 women with hormone receptor-positive, HER2-negative breast cancer received either fulvestrant and palbociclib or fulvestrant and an inactive substance called a placebo. All of the participants had metastatic cancer that had grown, spread, or come back after receiving hormonal therapy. Interestingly, 21% of the women had not yet gone through menopause. This is important because until now, only women who have been through menopause have received treatment with palbociclib in clinical trials.

When the researchers analyzed the data collected during the study, they found that the combination of fulvestrant and palbociclib kept breast cancer from growing or spreading for more than nine months compared with less than four months for fulvestrant treatment alone. The researchers also noted that the benefits of the combination treatment were similar whether the women had been through menopause or not. More time is needed to find out whether the fulvestrant and palbociclib combination will help women with metastatic hormone receptor-positive, HER2-negative breast cancer live longer.

What this means for patients

“After initial hormonal therapy stops working in metastatic breast cancer, the next step is typically chemotherapy, which can be effective, but the side effects are often very difficult for women,” said lead study author Nicholas C. Turner, MD, PhD, a consultant medical oncologist at The Royal Marsden and a team leader at The Institute of Cancer Research in London, United Kingdom. “This relatively easy-to-take new drug can substantially delay the point when women need to start chemotherapy, making this an exciting new approach for women.”

Earlier this year, the U.S. Food and Drug Administration approved treatment with palbociclib in combination with letrozole (Femara) under its accelerated approval program based on the results of a previous phase II study. Talk with your doctor for more information.

In this study, less than 3% of women had to stop treatment with fulvestrant and palbociclib because of side effects. The most common side effects of this combination were abnormal blood counts. Many of the women in this study developed low white blood cell counts, but very few (less than 1%) developed the more serious side effect of febrile neutropenia.

Questions to ask your doctor

  • What type and stage of breast cancer do I have? What does this mean?
  • What is the hormone status of my tumor? What is my HER2 status? How will this affect my treatment options?
  • Is palbociclib an option for me? Why or why not?
  • What treatment plan do you recommend? Why?
  • What clinical trials are open to me?
  • What are the possible side effects of each treatment, and how can they be managed?

More Information

Guide to Breast Cancer

Targeted Treatments