Ten Years of Tamoxifen Better Than 5 for Early-Stage, Estrogen-Receptor-Positive Disease

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After surgery and other treatments (chemotherapy, radiation therapy), women diagnosed with early-stage, hormone-receptor-positive breast cancer usually take 5 years of a hormonal therapy medicine to lower recurrence risk (the cancer coming back). When hormonal therapy is used this way, it's called adjuvant hormonal therapy.

Of the adjuvant hormonal therapy choices, tamoxifen has been approved the longest and is approved to treat both premenopausal and postmenopausal women. The other main type of hormonal therapy medicines are the aromatase inhibitors, which are approved to treat only postmenopausal women.

While most women take tamoxifen for 5 years, it hasn't been clear if taking tamoxifen for a longer time would offer more benefits.

Now new research has found that taking tamoxifen for 10 years instead of 5 years after surgery:

  • lowered the amount of breast cancer recurrence (the breast cancer coming back)
  • reduced the number of deaths from breast cancer
  • improved overall survival

The research was published online by The Lancet and presented at the 2012 San Antonio Breast Cancer Symposium on Dec. 5, 2012. Read the abstract of "Long-term effects of continuing adjuvant tamoxifen to 10 years versus stopping at 5 years after diagnosis of oestrogen receptor-positive breast cancer: ATLAS, a randomized trial."

Tamoxifen continues to be the recommended adjuvant hormonal therapy for PREmenopausal women diagnosed with hormone-receptor-positive, early-stage breast cancer. The aromatase inhibitors have become the recommended adjuvant hormonal therapy for POSTmenopausal women diagnosed with hormone-receptor-positive, early-stage breast cancer. Aromatase inhibitors are preferred over tamoxifen for postmenopausal women because a number of studies have shown that postmenopausal women treated with an aromatase inhibitor have a slightly lower recurrence risk than women treated with tamoxifen.

Called ATLAS (Adjuvant Tamoxifen: Longer Against Shorter), this large study randomly assigned nearly 13,000 women diagnosed with early-stage, hormone-receptor-positive breast cancer who had finished taking tamoxifen for 5 years to take it for another 5 years or to stop taking it.

The researchers then looked to see if recurrence risk was lower and survival was better in the nearly 7,000 women in the study diagnosed with estrogen-receptor-positive disease. The researchers also looked to see if tamoxifen caused side effects in any of the women.

The researchers found that recurrence risk 5 to 14 years after surgery was:

  • 21.4% for women who took tamoxifen for 10 years
  • 25.1% for women who took tamoxifen for 5 years

This means that taking tamoxifen for 10 years reduced recurrence risk by 3.7% compared to taking tamoxifen for 5 years.

Taking tamoxifen for 10 years also reduced the number of women who died from breast cancer:

  • 331 women who took tamoxifen for 10 years died from breast cancer
  • 397 women who took tamoxifen for 5 years died from breast cancer

Taking tamoxifen for 10 years versus 5 years also reduced the number of women that died from any cause during the study:

  • 639 women who took tamoxifen for 10 years died from any cause
  • 722 women who took tamoxifen for 5 years died from any cause

The researchers also found that these additional benefits from tamoxifen aren't seen until a woman has been taking tamoxifen for about 10 years.

Like any hormonal therapy medicine, tamoxifen can cause side effects, some of them serious. Hot flashes and night sweats are common tamoxifen side effects. In rare cases, tamoxifen can cause dangerous blood clots. Tamoxifen also may increase the risk of endometrial cancer in some women.

In this study, the researchers found that tamoxifen increased the risk of blood clots, but didn't increase the risk of having a stroke. Tamoxifen also slightly increased the risk of endometrial cancer. This increase in risk was higher in the women who took tamoxifen for 10 years compared to women who took tamoxifen for 5 years. Still, the benefits of taking tamoxifen for 10 years were much greater than the risks.

These results are extremely promising and likely to change the hormonal therapy standard of care for women diagnosed with early-stage, estrogen-receptor-positive breast cancer.

If you're a premenopausal women who's been diagnosed with early-stage, estrogen-receptor-positive breast cancer and are finishing up 5 years of tamoxifen, you may want to talk to your doctor about this study and whether taking tamoxifen for another 5 years (for a total of 10 years) makes sense for you. If your doctor doesn't recommend extending tamoxifen treatment, it's a good idea to ask why. Together, you can decide on a treatment plan that's best for YOU.

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