After surgery, women diagnosed with hormone-receptor-positive breast cancer usually take hormonal therapy medicine to reduce the risk of the cancer coming back (recurrence). Hormonal therapy medicines work in two ways:
- by lowering the amount of estrogen in the body
- by blocking the action of estrogen on breast cancer cells
There are several types of hormonal therapy medicines. Tamoxifen, a selective estrogen receptor modulator (SERM), is one of the most well-known. Tamoxifen can be used to treat both premenopausal and postmenopausal women. In the early 2000s, the aromatase inhibitors:
- Arimidex (chemical name: anastrozole)
- Aromasin (chemical name: exemestane)
- Femara (chemical name: letrozole)
were shown to be more effective at reducing recurrence risk in postmenopausal women and are now used more often than tamoxifen to treat women who’ve gone through menopause.
Aromatase inhibitors aren’t commonly used to reduce recurrence risk in premenopausal women. Still, in some cases a premenopausal woman may take medicine to suppress the function of her ovaries and take an aromatase inhibitor.
Both tamoxifen and aromatase inhibitors can cause side effects. Tamoxifen may cause hot flashes and increase the risk of blood clots and stroke. Aromatase inhibitors may cause muscle and joint aches and pains. Less common but more severe side effects of aromatase inhibitors are heart problems, osteoporosis, and broken bones.
A study has found that while the aromatase inhibitors don’t increase the risk of fatal heart attacks or strokes, the medicines do increase the risk of less serious heart problems, such as an abnormal heart beat or pericarditis (swelling of the membrane surrounding the heart), compared to tamoxifen.
The research was published online on April 21, 2016 by JAMA Oncology. Read the abstract of “Cardiovascular Disease After Aromatase Inhibitor Use.”
To do the study, the researchers looked at the medical records of 13,273 postmenopausal women who were diagnosed with hormone-receptor-positive breast cancer from 1991 to 2010. None of the women had a history of heart disease. The women were followed until December 2011, so the longest any woman was followed was 21 years and the shortest any woman was followed was 1 year.
The researchers grouped the women by the type of hormonal therapy they received:
- 31.7% were treated with only tamoxifen
- 28.6% were treated with only an aromatase inhibitor
- 20.2% received both types of hormonal therapy; meaning the women started on one type and then switched to the other
- 19.4% didn’t take hormonal therapy
The researchers also controlled for any other health problems the women had, as well as any other medicines the women were taking, both of which could affect their risk of heart problems.
Overall, the women had 3,711 cardiovascular events during the follow-up period.
Women who took only an aromatase inhibitor and women who took only tamoxifen had similar risks of:
- heart attack
- angina (chest pains)
Still, compared to women who took only tamoxifen or women who didn’t take hormonal therapy, the researchers found that women who took an aromatase inhibitor (either alone or after tamoxifen) had about a 27% higher risk of several less serious heart problems, including:
- abnormal heart beat
- problems with heart valve function
"Our study is a comprehensive assessment of the impact aromatase inhibitors have on cardiovascular risk and provides reassurance that the hormone therapy to reduce breast cancer recurrence does not increase risk of the most fatal cardiovascular events," said Reina Haque, Ph.D., MPH, research scientist with Kaiser Permanente and one of the study’s authors. "A particular strength of our study is that we accounted for women's other potential cardiovascular risk factors as well as medication used to treat high blood pressure and high cholesterol."
If you’re a postmenopausal woman diagnosed with hormone-receptor-positive breast cancer, keep two things in mind when you and your doctor are deciding on a hormonal therapy treatment plan after surgery:
- Every woman responds differently to treatment. What works for someone else may not work for you and what works for you may not work for someone else.
- Your treatment plan isn't written in stone. You can always switch medicines if another treatment has greater benefits and/or fewer side effects.
Aromatase inhibitors tend to cause fewer serious side effects than tamoxifen, such as blood clots, stroke, and endometrial cancer. But as this study suggests, aromatase inhibitors can cause more heart problems, as well as more bone loss (osteoporosis) and more broken bones, than tamoxifen, at least for the first few years of treatment. If you and your doctor are considering an aromatase inhibitor as part of your treatment plan, you may want to ask your doctor about having a bone density test to see if a bone strengthening medicine might be necessary while you're taking the aromatase inhibitor.
You also may want to ask your doctor about your personal risk of treatment-related heart problems and whether or not visiting a cardiologist before treatment starts is a good idea for you. The cardiologist can evaluate your heart function and decide if you’re at risk of developing heart disease or heart failure from breast cancer treatment. You also may want to ask your oncologist how your heart function will be monitored during treatment.
Together, you can decide on the best treatment plan for your unique situation.