Tamoxifen’s Benefits Long-Lasting for High-Risk Women

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After about 16 years of follow-up, a study shows that the hormonal therapy tamoxifen offered long-lasting breast cancer risk reduction for high-risk women who hadn’t been diagnosed with the disease.

The research was presented at the 2014 San Antonio Breast Cancer Symposium and published online by The Lancet Oncology on Dec. 11, 2014.

Read the abstract of “Tamoxifen for prevention of breast cancer: extended long-term follow-up of the IBIS-I breast cancer prevention trial.”

Tamoxifen is a SERM (selective estrogen receptor modulator). 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.

In this study, called the IBIS-I trial, 7,154 pre- and postmenopausal women at high risk for breast cancer but who hadn’t been diagnosed were randomly assigned to one of two treatments:

  • 20 milligrams of tamoxifen per day for 5 years (3,579 women)
  • placebo pill daily for 5 years (3,575 women)

The placebo pill was a sugar pill that looked exactly like the tamoxifen pill.

The women were between the ages of 35 and 70 and mostly had a higher risk of breast cancer because of a family history of the disease.

Half of the women were followed for more than 16 years and half of the women were followed for fewer than 16 years.

During the follow-up, fewer women in the tamoxifen group were diagnosed with breast cancer:

  • 246 women in the tamoxifen group were diagnosed
  • 343 women in the placebo group were diagnosed

This means that overall, tamoxifen reduced the risk of breast cancer by 29%.

The researchers looked at tamoxifen’s effects on the risk of specific types of breast cancer:

  • tamoxifen reduced the risk of estrogen-receptor-positive breast cancer by 35%
  • tamoxifen didn’t reduce the risk of estrogen-receptor-negative breast cancer

The researchers also looked to see if tamoxifen offered more benefits for women who didn’t take hormone replacement therapy:

  • tamoxifen reduced the risk of breast cancer by 38% in women who didn’t take hormone replacement therapy
  • tamoxifen reduced the risk of estrogen-receptor-positive disease by 45% in women who didn’t take hormone replacement therapy

“The International Breast Cancer Intervention Study-I was designed to investigate the long-term risks and benefits of taking tamoxifen to prevent breast cancer in women at high risk for developing the disease,” said Dr. Jack Cuzick, Ph.D., John Snow professor of epidemiology at the Wolfson Institute of Preventive Medicine at Queen Mary University of London. “We found that the reduction in breast cancer incidence remains strong and unabated for 20 years.”

Both the U.S. Preventive Services Task Force (USPSTF) and the American Society of Clinical Oncology (ASCO) recommend that doctors talk to women at high risk of breast cancer who haven’t been diagnosed about taking medicine to lower that risk.

The U.S. Preventive Services Task Force is a group of experts that makes recommendations to the U.S. Department of Health and Human Services on policies to prevent diseases. ASCO is a national organization of oncologists and other cancer care providers. ASCO guidelines give doctors recommendations for treatments and testing that are supported by much credible research and experience.

The most recent ASCO guidelines on using hormonal therapy to reduce breast cancer risk in high-risk women who haven’t been diagnosed recommend doctors to talk to premenopausal women at high risk about using tamoxifen or Evista (chemical name: raloxifene), another SERM, to reduce risk. For postmenopausal high-risk women, the guidelines recommend doctors discuss tamoxifen, Evista, and the aromatase inhibitor Aromasin (chemical name: exemestane) to reduce risk.

Both Evista and tamoxifen are approved by the U.S. Food and Drug Administration (FDA) to be used to prevent breast cancer in women who haven’t been diagnosed. Aromasin isn’t approved by the FDA to be used for breast cancer prevention. ASCO experts decided to recommend that it be discussed as a preventive medicine based on research showing that high-risk postmenopausal women who took Aromasin were 65% less likely to be diagnosed with breast cancer than women who took a placebo.

“For postmenopausal women, the aromatase inhibitors anastrozole [brand name: Arimidex] or exemestane are probably better alternatives, both in terms of greater effectiveness and better side-effect profiles, but for premenopausal women, tamoxifen remains the only choice and it is a good one,” said Dr. Cuzick.

Tamoxifen may cause some serious side effects, including blood clots, stroke, and endometrial cancer. Other common side effects of tamoxifen are:

  • hot flashes
  • night sweats
  • bone pain
  • nausea
  • fatigue
  • constipation
  • loss of libido
  • mood swings
  • depression
  • dry skin
  • hair thinning

As this and other studies have shown, tamoxifen is effective at reducing risk in high-risk women, but other research has found that it’s not widely prescribed by doctors or taken by women at high risk because of concerns about side effects.

To figure out if a woman has a higher-than-average risk of breast cancer, most doctors use some form of the Gail model, a standard breast cancer risk assessment tool. The Gail model assesses breast cancer risk based on a series of personal health questions that women and their doctors answer together. The questions ask about risk factors such as age, child-bearing history, family history of breast cancer, and breast biopsy results. The result is a Gail score, which estimates the risk of developing invasive breast cancer in the next 5 years. Some more recent versions of the Gail model also include alcohol use, menopausal status, and body mass index. Some doctors wonder if genetic testing or other information should be added to the Gail model. More research needs to be done to figure out the most accurate way to assess a woman’s risk of breast cancer.

If you have a higher-than-average risk of breast cancer, it makes sense to do everything 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
  • limiting processed foods and foods high in sugar
  • eating healthy, nutrient-dense food
  • not smoking

You and your doctor also may be considering medicine to reduce your risk. This study offers reassuring evidence that taking tamoxifen for 5 years offers benefits for many years after you stop taking the medicine.

Talk to your doctor about your preferences as well as the risks and benefits of each medicine you’re considering to reduce risk. If you’re a postmenopausal woman and already taking tamoxifen or Evista and having unacceptable side effects, you may want to ask if Aromasin might be a better option for you. Together, you can make the best choice for your unique situation.

You can learn more about using tamoxifen, Evista, or Aromasin to reduce risk in the Breastcancer.org Hormonal Therapy section.

Read more news from the 2014 San Antonio Breast Cancer Symposium:



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