Tamoxifen or exemestane after breast cancer? It’s trade-off, expert says

July 14, 2014 | by

The well-known drug tamoxifen might not always be the best choice for premenopausal women who have undergone treatment for breast cancer and face a heightened risk of recurrence. A new study suggests that the aromatase inhibitor exemestane, or Aromasin, works slightly better than tamoxifen in preventing cancer recurrence.

A new study finds aromatase inhibitors might be more effective than tamoxifen in preventing breast cancer relapse in premenopausal patients.

A new study finds that aromatase inhibitors might be more effective than tamoxifen in preventing breast cancer relapse in premenopausal patients.

Five years of tamoxifen is considered the standard of care for pre-menopausal women with hormone-receptor-positive breast cancer; aromatase inhibitors are often used in post-menopausal women.

But in a new study in the New England Journal of Medicine, nearly 93 percent of women on the aromatase inhibitor exemestane remained free of breast cancer after five years. About 89 percent of women on tamoxifen remained free of breast cancer over the same amount of time.  

No difference in overall survival was found between the two drugs. The study included nearly 4,700 women with breast cancer who had their ovarian function suppressed.

Both drugs come with no small risk of side effects. Exemestane, or Aromasin, can increase the risks of osteoporosis, vaginal dryness and lower sex drive. Tamoxifen, or Soltamox, can increase the risks of blood clots, hot flashes and urinary incontinence.

Now for some background on the drugs used for hormone receptor-positive breast cancer, which is fueled by estrogen:

  • Tamoxifen blocks estrogen from getting to cancer cells. Because it can also block estrogen circulating in the body, tamoxifen is usually used in breast cancer patients who have not gone through menopause.
  • Aromatase inhibitors stop other hormones from becoming estrogen. Because they work only when the ovaries are not producing estrogen, they typically have been given to postmenopausal women.

The new study indicates that aromatase inhibitors might also be an option for premenopausal women. But Joanne Mortimer, M.D., director of Women’s Cancer Programs at City of Hope, cautioned that there would be a trade-off in using aromatase inhibitors.

“It’s another option,” Mortimer said in a HealthDay interview. But “compared to aromatase inhibitors, the quality of life is better with tamoxifen for premenopausal women.”

The study, funded by the U.S. National Cancer Institute, Pfizer (which makes Aromasin), Ipsen (make of an ovarian suppression drug), and the International Breast Cancer Study Group, combined the results to two phase 3 clinical trials.

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Learn more about treatment and research for women's cancers at City of Hope.