A study suggests that the experimental medicine ribociclib (formerly called LEE011), given in combination with Femara (chemical name: letrozole), offers more benefits in treating advanced-stage, hormone-receptor-positive, HER2-negative breast cancer than Femara alone.
The study was presented at the 2016 European Society for Medical Oncology and published online at the same time on Oct. 8, 2016 in The New England Journal of Medicine. Read “Ribociclib as First-Line Therapy for HR-Positive, Advanced Breast Cancer.”
Like Ibrance (chemical name: palbociclib), ribociclib is a cyclin-dependent 4/6 kinase inhibitor. A kinase is a type of protein in the body that helps control cell division. Ribociclib works by stopping cancer cells from dividing and growing.
Femara is an aromatase inhibitor, a type of hormonal therapy medicine. Femara works by stopping the production of estrogen in postmenopausal women. This means that less estrogen is available to stimulate the growth of hormone-receptor-positive breast cancer cells.
Both ribociclib and Femara are pills taken by mouth.
The study, called MONALEESA-2, included 668 postmenopausal women from 29 countries diagnosed with hormone-receptor-positive, HER2-negative, recurrent or metastatic breast cancer. Recurrent breast cancer is breast cancer that comes back after treatment is completed. Metastatic breast cancer is breast cancer that has spread to an area of the body away from the breast, such as the bones or liver. None of the women had received treatment for the advanced-stage breast cancer.
The women were randomly split into two groups:
- 334 women were treated with ribociclib (600 mg per day on a 3-weeks on, 1-week-off schedule), plus Femara (2.5 mg per day)
- 334 women were treated with a placebo plus Femara; the placebo was a sugar pill that looked just like ribociclib
The women took the medicines until the cancer grew or unacceptable side effects developed.
After about 15.3 months of follow-up, women who were treated with ribociclib and Femara had about 44% better progression-free survival than women treated with Femara alone.
Progression-free survival is how long the women lived without the cancer growing.
After 18 months of follow-up:
- 63% of the women treated with ribociclib and Femara were alive without the cancer growing
- 42.2% of the women treated with Femara alone were alive without the cancer growing
About 53% of the women treated with ribociclib and Femara responded to the treatment, compared to about 37% of women treated with Femara alone.
Women treated with ribociclib and Femara had more side effects than women treated only with Femara:
- 59% of women treated with ribociclib had neutropenia (low counts of a specific type of white blood cell) compared to 1% of women treated with Femara alone
- 21% of women treated with ribociclib had leukopenia (low counts of a different type of white blood cell) compared to 1% of women treated with Femara alone
- 7% of women treated with ribociclib had lymphopenia (low counts of another type of white blood cell) compared to 1% of women treated with Femara alone
Women treated with ribociclib also had more serious side effects than women treated with Femara alone:
- 81.2% of women treated with ribociclib had a serious side effect
- 32.7% of women treated with Femara alone had a serious side effect
While these results are encouraging, the researchers want to do more studies to figure exactly who will benefit the most from ribociclib.
"Further study is required to determine which patients will benefit most from treatment," said Gabriel Hortobagyi, M.D., of the University of Texas MD Anderson Cancer Center and lead author of the study. Dr. Hortobagyi also is a member of the Breastcancer.org Professional Advisory Board. "The problem is that we don't have biomarkers," he continued. "We do not know whether 100% of patients benefit, or 50% or 30% or 20%, so we cannot select a patient population to enrich. We are working very hard on developing such biomarkers, but those do not exist at this point."
If you’re being treated for advanced-stage, hormone-receptor-positive, HER2-negative breast cancer that has come back or grown while being treated with hormonal therapy, you may want to talk to your doctor about this study. Treatment with a regimen that includes a cyclin-dependent 4/6 kinase inhibitor, such as experimental ribociclib in a clinical trial or Ibrance, which was approved by the U.S. Food and Drug Administration in 2015, may be an option for you, depending on your unique situation.
Stayed tuned to Breastcancer.org for the latest information on ribociclib and how it’s being used to treat breast cancer.