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 2006, 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.
Most women take hormonal therapy for 5 to 10 years after breast cancer surgery.
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. Research has shown that about 25% of women who are prescribed hormonal therapy to reduce the risk of recurrence after surgery either don’t start taking the medicine or stop taking it early, in many cases because of side effects.
A study has found that postmenopausal women who stop taking hormonal therapy early or skip doses are much more likely to have a breast cancer recurrence than women who take hormonal therapy as prescribed.
The research was published online on May 23, 2016 by the Journal of Clinical Oncology. Read the abstract of “Treatment Adherence and Its Impact on Disease-Free Survival in the Breast International Group 1-98 Trial of Tamoxifen and Letrozole, Alone and in Sequence.”
In this study, the researchers analyzed information that was collected as part of the BIG 1-98 study that was open from 1999 to 2003. The BIG 1-98 study was designed to see which hormonal therapy treatment was most effective:
- 5 years of Femara alone
- 5 years of tamoxifen alone
- 2 years of tamoxifen followed by 3 years of Femara
- 2 years of Femara followed by 3 years of tamoxifen
for postmenopausal women diagnosed with hormone-receptor-positive disease.
To do this study, the researchers analyzed information on persistence and compliance for 6,144 women in the BIG 1-98 study:
- “persistence” is how long the women took the hormonal therapy; all the women were prescribed hormonal therapy for 60 months -- any woman who took hormonal therapy for at least 54 months was considered to have completed the full course of treatment
- “compliance” is how consistent the women were in taking the hormonal therapy; the women were given treatment packs every 6 months -- any woman who took at least 80% of the pills during each 6-month period and took no treatment breaks that were 7 days or longer was considered to be compliant with treatment
The researchers wanted to see if women who were considered persistent and compliant had better disease-free survival than women who were not persistent and compliant.
Disease-free survival was defined as how long the women lived without the cancer coming back or a new cancer being diagnosed in the opposite breast.
The women were evenly split among the different hormonal therapy treatments:
- 1,541 women received 5 years of Femara
- 1,535 women received 5 years of tamoxifen
- 1,541 women received 2 years of tamoxifen followed by 3 years of Femara
- 1,527 women received 2 years of Femara followed by 3 years of tamoxifen
Overall, about 19% of the women didn’t complete the prescribed course of hormonal therapy.
The percentages of women who didn’t complete the prescribed course of therapy by treatment type were:
- 17.5% of women prescribed 5 years of Femara didn’t complete treatment
- 17% of women prescribed 5 years of tamoxifen didn’t complete treatment
- 21% of women prescribed 2 years of tamoxifen then 3 years of Femara didn’t complete treatment
- 20% of women prescribed 2 years of Femara then 3 years of tamoxifen didn’t complete treatment
Women who stopped taking hormonal therapy early were 35% to 56% more likely to have a recurrence than women who didn’t stop taking the medicine early.
Overall, 5.1% of the women were not compliant with the hormonal therapy.
The percentages of women who weren’t compliant by treatment type were:
- 4.5% of women prescribed 5 years of Femara weren’t compliant
- 5.7% of women prescribed 5 years of tamoxifen weren’t compliant
- 5.2% of women prescribed 2 years of tamoxifen then 3 years of Femara weren’t compliant
- 5.3% of women prescribed 2 years of Femara then 3 years of tamoxifen weren’t compliant
Women who weren’t compliant with hormonal therapy were 61% more likely to have a recurrence than women who were compliant.
Most of the women who stopped taking hormonal therapy early -- about 83% -- said they stopped taking the medicine because of side effects. Women who took Femara then tamoxifen or tamoxifen then Femara were more likely to stop taking hormonal therapy early.
Joint pain was the most common reason women stopped taking Femara early. Blood clots were the most common reason women stopped taking tamoxifen early.
- were older
- smoked or were former smokers
- had been diagnosed with node-negative disease (no cancer cells were found in the lymph nodes)
- had a history of blood clots
- switched from one hormonal therapy to the other
were more likely to stop treatment early.
If you’re a postmenopausal woman who’s been diagnosed with hormone-receptor-positive breast cancer and will be taking hormonal therapy after surgery and other treatments, it’s very important that you take the medicine for as long as it’s prescribed and at the dose at which it is prescribed. Hormone-receptor-positive breast cancer can come back and hormonal therapy after surgery reduces that risk -- you must remember that.
Side effects caused by hormonal therapy can be very troublesome for many women. It’s important to talk to your doctor as soon as you start having any side effects, including hot flashes, joint pain, blood clots, trouble sleeping, fatigue, or difficulty concentrating. Don’t wait until the symptoms are intolerable and you have to stop taking the medicine. There are steps you can take to ease these side effects, including switching to a different type of hormonal therapy.
For more information, visit the Breastcancer.org pages on Staying on Track With Treatment. You can read about why it’s so important to stick to your treatment plan, as well as ways to manage side effects after radiation, chemotherapy, and hormonal therapy. If you’re taking hormonal therapy after surgery now, stick with it as prescribed. If you’re thinking of stopping early, talk to your doctor first. Together, you can find a solution that is best for you.