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Many Younger Women Don’t Take Tamoxifen as Prescribed for Breast Cancer

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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

A study has found that more than 18% of premenopausal women diagnosed with early-stage, hormone-receptor-positive breast cancer were not taking hormonal therapy as prescribed, including more than 13% who were not taking the medicine at all.

The research was presented on Oct. 19, 2018 at the European Society for Medical Oncology 2018 Congress. Read the abstract of “Serum assessment of non-adherence to adjuvant endocrine therapy (ET) among premenopausal patients in the prospective multicenter CANTO cohort.”

Hormonal therapy reduces recurrence risk

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.

Still, like most cancer medicines, 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.

Other 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. This is the first study to look at hormonal therapy adherence in younger women.

Assessing adherence through blood levels of tamoxifen

This study included 1,799 premenopausal women who had been diagnosed with early-stage, hormone-receptor-positive breast cancer and who were part of the CANTO cohort, a French study looking at the long-term effects of breast cancer treatment.

All the women agreed to take hormonal therapy medicine:

  • 83.2% of the women were prescribed tamoxifen.
  • 1.4% of the women were prescribed tamoxifen and a luteinizing hormone-releasing hormone, a medicine that shuts down the ovaries.
  • 7.5% of the women were prescribed an aromatase inhibitor and a luteinizing hormone-releasing hormone.

For 7.9% of women, the type of hormonal therapy medicine prescribed was unknown.

To determine how well the women prescribed tamoxifen were sticking to their hormonal therapy treatment plan, the researchers measured the level of tamoxifen in the women’s blood, rather than asking them how they took tamoxifen. This is the first study to measure adherence this way.

Overall, 18.2% of the women were not taking tamoxifen as prescribed:

  • 13.2% had no detectable levels of tamoxifen in their blood, suggesting they were not taking the medicine at all.
  • 5.0% had tamoxifen levels lower than expected, suggesting they were not taking the medicine every day.

“I was surprised at the high rate of non-adherence, which was considerably higher than reported previously,” said lead author Barbara Pistilli, medical oncologist at Institut Gustave Roussy, Villejuif, France, in a statement. “Women with breast cancer should be encouraged to discuss their treatment and any side effects they experience with their doctor to obtain help to take their therapy.”

Staying on track with treatment

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 extremely 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 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.

To talk with others about staying on track with hormonal therapy treatment, join the Discussion Board forum Hormonal Therapy - Before, During, and After.

Written by: Jamie DePolo, senior editor

Reviewed by: Brian Wojciechowski, M.D., medical adviser

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