Hormonal Therapy After Surgery Reduces Risk of Breast Cancer in Opposite Breast in Real-World Setting

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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

Doctors call treatments taken after surgery “adjuvant” treatments.

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.

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 women in a general community setting diagnosed with hormone-receptor-positive breast cancer who took hormonal therapy after surgery had a lower risk of breast cancer in the opposite breast -- doctors call this contralateral breast cancer. The study also found that the risk of contralateral disease got progressively lower the longer a woman took hormonal therapy.

The research was published online on Oct. 6, 2016 by JAMA Oncology. Read the abstract of “Association of Adjuvant Tamoxifen and Aromatase Inhibitor Therapy With Contralateral Breast Cancer Risk Among US Women With Breast Cancer in a General Community Setting.”

Many studies have shown that women diagnosed with hormone-receptor-positive breast cancer who take hormonal therapy after surgery have a lower risk of developing breast cancer in the other breast. But as the researchers who did this study point out, the results of a study done in a very controlled clinical environment aren’t always achieved in the real world. For example, in clinical studies, women have to document that they took the complete course of hormonal therapy. In the real world, we know that many women stop taking hormonal therapy early or may stop taking the medicine for a long period of time and then start taking it again.

So the researchers wanted to measure the benefits of hormonal therapy in a real-world setting.

To do the study, the researchers looked at the records of 7,541 women diagnosed with breast cancer between 1990 and 2008. The women lived in Colorado or Oregon.

The women ranged in age from about 25 to about 85; about 93% of the women were white. The researchers had about 6 years of follow-up information on the women.

About half the women in the study took tamoxifen:

  • 52% of the women (3,900 women) took tamoxifen -- half the women took the medicine for fewer than 3.3 years and half the women took the medicine for longer than 3.3 years
  • About 25% of the women (1,929 women) took an aromatase inhibitor:
    • 963 women took both tamoxifen and an aromatase inhibitor -- half the women took hormonal therapy for fewer than 2.2 years and half the women took hormonal therapy for longer than 2.2 years
    • 966 women took only an aromatase inhibitor -- half the women took the medicine for fewer than 2.9 years and half the women took the medicine for longer than 2.9 years

During follow-up, 248 women were diagnosed with breast cancer in the other breast:

  • 45 cancers were DCIS
  • 203 cancers were invasive disease

The researchers’ analysis showed that the risk of developing breast cancer in the opposite breast decreased the longer a woman took tamoxifen. Compared to women who didn’t take hormonal therapy, women who took tamoxifen for 4 years had a 66% lower risk of developing breast cancer in the other breast.

And the benefits of tamoxifen lasted: Even 5 years after a woman stopped taking tamoxifen, her risk of contralateral breast cancer was lower than a woman who had never taken hormonal therapy.

Women who took only an aromatase inhibitor had about a 52% lower risk of developing breast cancer in the opposite breast compared to women who didn’t take hormonal therapy.

If you’ve 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, such as 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.



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