A study has found that the experimental targeted therapy medicine abemaciclib in combination with either the aromatase inhibitors Arimidex (chemical name: anastrozole) or Femara (chemical name: letrozole) improved progression-free survival in postmenopausal women diagnosed with hormone-receptor-positive, HER2-negative, advanced-stage breast cancer.
Progression-free survival is how long the women lived without the cancer growing.
The research was presented on Sept. 10, 2017 at the 2017 European Society for Medical Oncology Congress.
Like Ibrance (chemical name: palbociclib) and Kisqali (chemical name: ribociclib), abemaciclib is a cyclin-dependent 4/6 kinase inhibitor. A kinase is a type of protein in the body that helps control cell division. Abemaciclib works by stopping cancer cells from dividing and growing. Abemaciclib is a pill taken by mouth.
Advanced-stage cancer is breast cancer that has spread beyond the breast to nearby tissues, such as the skin or the chest wall, or that has spread to parts of the body away from the breast, such as the bones or liver.
In the study, called MONARCH 3, the researchers randomly assigned 493 postmenopausal women diagnosed with hormone-receptor-positive, HER2-negative, advanced-stage breast cancer to one of two treatments:
- abemaciclib plus Arimidex or Femara
- placebo (a dummy pill that looked just like abemaciclib) plus Arimidex or Femara
None of the women had been treated with hormonal therapy or chemotherapy for advanced-stage disease.
The resulted showed:
- 59% of the women had some response to the abemaciclib combination treatment
- 44% of the women had some response to the aromatase inhibitor alone treatment
Women treated with abemaciclib plus an aromatase inhibitor were 46% less likely to have the cancer grow compared to women treated with only an aromatase inhibitor alone.
This difference was statistically significant, which means that it was likely due to the difference in treatments and not just because of chance.
“This is the third study demonstrating that the combination of endocrine therapy with a CDK4/6 inhibitor is better than endocrine therapy alone,” said lead author Angelo Di Leo, medical oncologist, Sandro Pitigliani Medical Oncology Department, Hospital of Prato. “Abemaciclib reduced the risk of disease progression by 46%.”
The results also suggest that abemaciclib may offer benefits to women with more aggressive disease. In women diagnosed with breast cancer that had spread to the liver, abemaciclib improved progression-free survival more than an aromatase inhibitor alone. In women diagnosed with breast cancer that had spread to the bones and women diagnosed with breast cancer that had come back years after initial hormonal therapy treatment ended, which is considered less aggressive, an aromatase inhibitor alone offered about the same results as an aromatase inhibitor plus abemaciclib.
“Now for the first time, we have insights suggesting that patients with certain clinical characteristics may benefit differently from treatment with a CDK 4/6 inhibitor, including the possibility that some patients with a good prognosis may be able to start on endocrine therapy alone," Di Leo continued. “In such patients, CDK4/6 inhibitors could potentially be reserved as a next line of treatment for metastatic disease. This idea warrants further study given our data."
Like almost all cancer medicines, abemaciclib can cause side effects, some of them severe. Women treated with abemaciclib were more likely to have side effects than women treated with an aromatase inhibitor alone. The most common side effects were:
- diarrhea: 81.3% of women treated with abemaciclib compared to 29.8% of women treated with an aromatase inhibitor alone
- low white blood cell counts (neutropenia): 41.3% of women treated with abemaciclib compared to 1.9% of women treated with an aromatase inhibitor alone
- fatigue: 40.1% of women treated with abemaciclib compared to 31.7% of women treated with an aromatase inhibitor alone
Compared to Ibrance and Kisqali, abemaciclib seems to cause less neutropenia, but more ongoing diarrhea.
If you’ve been diagnosed with advanced-stage, hormone-receptor-positive, HER2-negative breast cancer, you may want to talk to your doctor about this study. While abemaciclib is still an experimental medicine, Eli Lilly, the company that makes abemaciclib, has said that it plans to submit marketing applications for the medicine to the U.S. Food and Drug Administration (FDA) for breast cancer treatment this year. Abemaciclib also is being studied to treat lung and pancreatic cancer.
Stayed tuned to Breastcancer.org for the latest information on abemaciclib and any FDA approvals for breast cancer treatment.