Afinitor (chemical name: everolimus) is approved to be used in combination with the aromatase inhibitor Aromasin (chemical name: exemestane) to treat advanced-stage, hormone-receptor-positive, HER2-negative breast cancer in postmenopausal women that has already been treated with the aromatase inhibitors Femara (chemical name: letrozole) or Arimidex (chemical name: anastrozole).
A targeted therapy medicine, Afinitor is an mTOR (mammalian target of rapamycin) inhibitor. mTOR is a kinase, a type of protein in the body. Kinases help all cells -- both healthy and cancer cells -- get the energy they need. When kinases don’t act normally or are overactive, they help certain breast cancers grow. mTOR inhibitors work by interfering with the mTOR kinase. Afinitor is a pill taken by mouth.
Metastatic breast cancer is advanced-stage breast cancer that has spread to part of the body away from the breast, such as the bones or liver.
Hormonal therapy, often an aromatase inhibitor, is the standard of care for women diagnosed with advanced-stage, hormone-receptor-positive disease. Still, a number of these type of cancers become resistant to aromatase inhibitors over time. So doctors have been looking for other treatment options.
A study suggests that adding Afinitor to the hormonal therapy Faslodex (chemical name: fulvestrant) can help treat metastatic, hormone-receptor-positive, HER2-negative breast cancer that has become resistant to aromatase inhibitors.
The research was presented on Dec. 7, 2016 at the 2016 San Antonio Breast Cancer Symposium. Read the abstract of “PrECOG 0102: A randomized, double-blind, phase II trial of fulvestrant plus everolimus or placebo in postmenopausal women with hormone-receptor (HR)-positive, HER2-negative metastatic breast cancer (MBC) resistant to aromatase inhibitor (AI) therapy.”
Faslodex is a type of hormonal therapy called an estrogen receptor downregulator (ERD). It blocks the effects of estrogen in breast tissue, but doesn’t lower the amount of estrogen in the body like the aromatase inhibitors.
The study included 130 postmenopausal women diagnosed with metastatic hormone-receptor-positive, HER2-negative breast cancer that had become resistant to aromatase inhibitors. About half the women were older than 61 and half the women were younger.
The women were randomly assigned to received one of two treatments:
- Faslodex plus Afinitor (64 women)
- Faslodex plus placebo (a dummy pill that looked just like Afinitor) (66 women)
Neither the researchers nor the women in the study knew which women got which treatment.
The researchers wanted to see if adding Afinitor to Faslodex would improve progression-free survival, the length of time the women lived without the cancer growing.
- Women treated with Faslodex and Afinitor lived for 10.4 months without the cancer growing.
- Women treated with Faslodex and placebo lived for 5.1 months without the cancer growing.
This difference was statistically significant, which means that it was likely because of the difference in treatment and not just due to chance.
Still, women treated with Afinitor had more severe side effects, including:
- extremely high blood sugar levels: 16% in the Afinitor group vs. 0% in the placebo group
- mouth sores: 11% in the Afinitor group vs. 0% in the placebo group
- high triglyceride levels: 9% in the Afinitor group vs. 0% in the placebo group
- low white blood cell counts: 9% in the Afinitor group vs. 0% in the placebo group
- inflammation in the lungs: 6% in the Afinitor group vs. 0% in the placebo group
Overall, 39% of women treated with Faslodex and Afinitor stopped taking the medicines because of side effects, their doctor’s suggestion, or other reasons, compared to 21% of women treated with Faslodex and placebo.
"The rates of grade 3/4 adverse events in our study are very similar to those found in earlier studies evaluating combination therapies containing everolimus," said Noah Kornblum, M.D., assistant professor of medicine at Albert Einstein College of Medicine and lead author of the study. "It is important for patients and clinicians to be aware of these potential complications, to try to identify them early, and to learn ways to manage them. For example, recently we have learned that the use of prophylactic corticosteroid mouthwash could significantly reduce the risk of oral mucositis for some patients taking everolimus."
While the results of this study are promising, this study was small. More research is needed on combining Faslodex and Afinitor to treat metastatic, hormone-receptor-positive breast cancer before it becomes the standard of care.
"We have to resist temptation to immediately adopt a positive result of a novel combination from a small study into a new standard of care," said Kornblum. "It may one day be the case that everolimus and fulvestrant become a new approved therapy for metastatic hormone-receptor-positive breast cancer, but caution is prudent until larger studies confirm our results."
If you have been diagnosed with metastatic, hormone-receptor-positive, HER2-negative breast cancer that has stopped responding to an aromatase inhibitor, you and your doctor are likely considering a number of treatment options. You may want to talk to your doctor about this study and ask if Afinitor should be considered for your unique situation.