Both tamoxifen and Evista (chemical name: raloxifene) are hormonal therapy medicines and have been shown to lower the risk of breast cancer in women at high risk for breast cancer because of strong family history or a known abnormal gene.
A study has found that most high risk women either refuse to take preventive Evista or tamoxifen or stop taking the medicine early.
The study was published online on Dec. 8, 2015 by the Annals of Oncology. Read the abstract of “Factors affecting uptake and adherence to breast cancer chemoprevention: a systematic review and meta-analysis.”
Tamoxifen and Evista are both SERMs (selective estrogen receptor modulators), a type of hormonal therapy medicine. SERMs block the action of estrogen in breast and certain other cells by sitting in the cells’ estrogen receptors. SERMs don’t affect all estrogen receptors the same way because they’re selective (as the name says). In bone cells, SERMs interact with the receptors the way estrogen does and strengthen bones. In breast cells, SERMs block the receptors’ interaction with estrogen and limit cell growth.
As medicines to lower the risk of breast cancer in high-risk women who have never been diagnosed, tamoxifen and Evista are often taken for 5 years.
This study was a meta-analysis -- a study that combines and analyzes the results of earlier studies. In this case, the researchers analyzed 26 studies looking at how well women at high risk for breast cancer stuck to their preventive medicine treatment plan. More than 21,420 women participated in the 26 studies.
In the studies, the women were prescribed tamoxifen, Evista, or a placebo (a sugar pill that looked just like tamoxifen or Evista).
In 2013, the American Society of Clinical Oncology put out new guidelines on using hormonal therapy medicines to reduce breast cancer risk in high-risk undiagnosed women. Besides tamoxifen and Evista, the guidelines also recommend that doctors talk to postmenopausal high-risk women about using the aromatase inhibitor Aromasin (chemical name: exemestane) to reduce risk. Also, other research has shown that the aromatase inhibitor Arimidex (chemical name: anastrozole) can lower the risk of first-time, hormone-receptor-positive breast cancer in postmenopausal women at high risk who haven’t been diagnosed. Arimidex isn’t approved by the U.S. Food and Drug Administration for this use, but doctors may consider it a good alternative to other hormonal therapies approved to reduce risk in high-risk postmenopausal women.
While it’s not clear exactly when the studies included in the meta-analysis were done, none of them included either Aromasin or Arimidex as a medicine to lower breast cancer risk in high-risk women that hadn’t been diagnosed.
Overall, the researchers found that only about 16% of high risk women took the full course of preventive hormonal therapy medicine.
Women who were enrolled in a clinical trial were somewhat more likely to stick to their preventive medicine treatment plan:
- more than 25% of women in clinical trials completed the full course of hormonal therapy
- only about 9% of women who weren’t in a clinical trial completed the full course of hormonal therapy
Women were more likely to complete the full course of preventive hormonal therapy if they:
- had an abnormal breast biopsy
- had the preventive medicine recommended by a doctor
- had much higher than average risk
- had fewer side effects
Women were less likely to complete the full course of preventive hormonal therapy if they:
- were taking tamoxifen
- were depressed
“Our…research reveals that only a small portion of eligible women make the decision to have preventative medication,” said Dr. Sam Smith, of the Wolfson Institute of Preventive Medicine at Queen Mary University of London and lead author of the study said in a statement. “It’s crucial to find out why so many chose not to take the drugs -- or stopped taking them before completing the course.”
Both tamoxifen and Evista can cause side effects, some of them serious. Common side effects associated with tamoxifen are:
- blood clots
- a higher risk of endometrial cancer
- leg cramps
- weight gain
- hot flashes
- joint pain
While Evista also may cause blood clots and stroke, women taking Evista are less likely to have these two serious side effects compared to women taking tamoxifen. Evista also may cause:
- hot flashes
- joint pain
- weight gain
Aromasin and Arimidex also may cause side effects, including hot flashes and bone and joint pain.
Earlier studies suggest these side effects may be a big part of the reason many women decide not to take tamoxifen or Evista (or stop taking the medicine early) to reduce breast cancer risk.
The researchers who did this meta-analysis said that more research is needed to figure out exactly why women don’t start or stop these preventive medicines early.
If you have a higher-than-average risk of breast cancer, it makes sense to do all that you can to keep your risk as low as it can be. There are lifestyle choices you can make, including:
- maintaining a healthy weight
- exercising regularly at the highest intensity possible
- limiting or avoiding alcohol
- not smoking
- eating a diet that is full of fresh, nutrient-dense foods and low in processed food and foods high in sugar
You and your doctor also may be considering medicine to reduce your risk. Talk to your doctor about your preferences as well as the risks and benefits of each medicine. If you’re a postmenopausal woman and already taking tamoxifen or Evista and having unacceptable side effects, you may want to ask if Aromasin or Arimidex might be a better option for you. Together, you can make the best choice for your unique situation.
You can learn more about medicines to reduce risk in high-risk women who haven’t been diagnosed in the Breastcancer.org Hormonal Therapy section.