Another Study Shows Ten Years of Tamoxifen Better Than Five 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.

In December 2012, results from the ATLAS study were presented at the San Antonio Breast Cancer Symposium showing 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

Now another large study has found similar results: 10 years of tamoxifen is better than 5.

The study, "Long-term effects of continuing adjuvant tamoxifen to 10 years versus stopping at 5,” was presented June 1, 2013 at the 2013 American Society of Clinical Oncology Annual Meeting.

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 aTTOM (Adjuvant Tamoxifen – to Offer More?), this large United Kingdom study randomly assigned nearly 7,000 women diagnosed with early-stage, estrogen-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 either group of women. The researchers also looked to see if 10 years of tamoxifen caused side effects in any of the women.

The researchers found:

  • 580 women who took tamoxifen for 10 years had a recurrence
  • 672 women who took tamoxifen for 5 years had a recurrence

This difference was significant, which means that it was likely because of the extra 5 years of tamoxifen and not just due to chance.

  • 392 women who took tamoxifen for 10 years died after recurrence
  • 443 women who took tamoxifen for 5 years died after recurrence

Overall, 10 years of tamoxifen reduced breast cancer recurrence and death rates by an extra 25%, compared to 5 years of tamoxifen.

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 10 years tamoxifen increased the risk of endometrial cancer compared to 5 years of tamoxifen. Still, the benefits of taking tamoxifen for 10 years outweighed the risks.

Combined with the results of the ATLAS trial, 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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