Arimidex Still Better Than Tamoxifen After Surgery to Reduce Recurrence Risk

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After surgery and other treatments for early-stage, hormone-receptor-positive breast cancer, many postmenopausal women take hormonal therapy medicine -- either an aromatase inhibitor or tamoxifen -- to reduce the risk of the cancer coming back (recurrence).

The aromatase inhibitors are:

  • Arimidex (chemical name: anastrozole)
  • Aromasin (chemical name: exemestane)
  • Femara (chemical name: letrozole)

After 10 years of follow-up, a study shows that taking Arimidex for 5 years is better at reducing the risk of hormone-receptor-positive breast cancer recurrence than taking tamoxifen for 5 years. These results were presented at the 2010 American Society of Clinical Oncology (ASCO) Breast Cancer Symposium.

The results are the latest analysis from the large ATAC (Arimidex and Tamoxifen Alone or in Combination) study. The ATAC study compared Arimidex to tamoxifen in 6,241 postmenopausal women diagnosed with hormone-receptor-positive breast cancer. Earlier ATAC results found that Arimidex was more effective than tamoxifen in reducing the risk of recurrence of early-stage, hormone-receptor-positive breast cancer in postmenopausal women. Other studies comparing tamoxifen to the other two aromatase inhibitors (Aromasin and Femara) have shown similar results.

Earlier ATAC results showed that women taking Arimidex had an overall lower risk of recurrence compared to women taking tamoxifen. These latest ATAC results found the link between lower risk of recurrence and Arimidex continued.

Five years after diagnosis:

  • 9.8% of women who took Arimidex for 5 years had a recurrence
  • 12.5% of women who took tamoxifen for 5 years had a recurrence

Ten years after diagnosis:

  • 19.7% of women who took Arimidex for 5 years had a recurrence
  • 24% of women who took tamoxifen for 5 years had a recurrence

This means that women taking Arimidex after surgery and other treatments were 21% less likely than women taking tamoxifen to have a recurrence over 10 years (5 years after finishing hormonal therapy treatment).

Earlier ATAC results also showed that women taking Arimidex had a lower risk of the cancer coming back in a part of the body away from the breast (called distant or metastatic recurrence) compared to women taking tamoxifen. These latest results showed this link between lower distant recurrence risk and Arimidex continued.

Five years after diagnosis:

  • 7.9% of women who took Arimidex for 5 years had a distant recurrence
  • 9.2% of women who took tamoxifen for 5 years had a distant recurrence

Ten years after diagnosis:

  • 15.1% of women who took Arimidex for 5 years had a distant recurrence
  • 17.7% of women who took tamoxifen for 5 years had a distant recurrence

This means that women taking Arimidex after surgery and other treatments were 15% less likely than women taking tamoxifen to have a distant recurrence over 10 years (5 years after finishing hormonal therapy treatment).

The latest ATAC analysis also found that the overall risk of side effects (both serious and not-so-serious) was lower for Arimidex compared to tamoxifen. Earlier ATAC results showed that serious side effects were less common in women taking Arimidex compared to women taking tamoxifen. Still, the latest analysis showed that this evened out and the risk of serious side effects was about the same for both Arimidex and tamoxifen.

The risk of bone fractures and joint pain were slightly higher for women taking Arimidex compared to women taking tamoxifen in earlier ATAC analyses (when the women were actually taking the medicines). In the latest analysis (5 years after the women stopped taking the medicines), the risk of bone fractures were the same. This means that the higher risk of breaking a bone while taking Arimidex went down after women finished taking Arimidex.

Although the likelihood of dying from breast cancer was slightly lower in women who took Arimidex compared to women who took tamoxifen, this difference wasn't statistically significant. This means the difference could have been due chance and not because of the difference in treatments.

Based on these and other results, ASCO issued new guidelines on adjuvant hormonal therapy medicines (hormonal therapy given after surgery and other treatments) in July 2010. ASCO is a national organization of oncologists and other cancer care providers. The guidelines recommend that an aromatase inhibitor usually is preferred over tamoxifen as adjuvant hormonal therapy and usually should be taken for 5 years. The guidelines don't recommend one aromatase inhibitor over another.

While the ASCO guidelines recommend an aromatase inhibitor as adjuvant hormonal therapy for postmenopausal women diagnosed with early-stage, hormone-receptor-positive breast cancer, tamoxifen may still be a good choice for some women for a number of reasons, including side effects and cost.

If adjuvant hormonal therapy will be part of your breast cancer treatment, you may want to ask your doctor about the risks and benefits of aromatase inhibitors and tamoxifen. Your doctor will consider a number of factors when recommending one or the other, as well as how long you should take hormonal therapy.

When you're deciding on a treatment plan, keep two things in mind:

  • Every woman responds differently to treatment. What works for someone else may not work for you and what works for you may not work for someone else.
  • Your treatment plan isn't written in stone. You can always change treatments if another treatment has greater benefits and fewer side effects.

Together, you and your doctor will decide on the treatment plan that makes the most sense for your unique situation.

Visit the Breastcancer.org Hormonal Therapy section to learn more about tamoxifen, aromatase inhibitors, and adjuvant therapy.

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