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Arimidex (chemical name: anastrozole) is an aromatase inhibitor approved by the U.S. Food and Drug Administration (FDA) to treat:

  • postmenopausal women diagnosed with hormone-receptor-positive, early-stage breast cancer after surgery (or possibly chemotherapy and radiation) to reduce the risk of the cancer coming back
  • postmenopausal women diagnosed with advanced-stage or metastatic hormone-receptor-positive breast cancer 

Arimidex won't work on hormone-receptor-negative breast cancer. Arimidex shouldn't be taken at the same time as tamoxifen.

Arimidex is a pill taken once a day. Most doctors recommend taking Arimidex at the same time each day.

Benefits of Arimidex

Since 1999, researchers have been conducting the large ATAC (Arimidex, Tamoxifen Alone or in Combination) trial to compare Arimidex to tamoxifen after surgery. The researchers are looking at how the medicines work by themselves as well as together to see which combination is the best treatment for postmenopausal women diagnosed with early-stage, hormone-receptor-positive breast cancer. Based on initial results of this trial, giving Arimidex and tamoxifen at the same time isn't recommended.

So far, the results show that 5 years of Arimidex is better than 5 years of tamoxifen as the first hormonal therapy for postmenopausal women with early-stage, hormone-receptor-positive breast cancer. Arimidex is better than tamoxifen for:

  • increasing the time before the cancer comes back in those who experience recurrence
  • reducing the risk of the cancer spreading to other parts of the body
  • reducing the risk of a new cancer developing in the other breast

Research presented at the 2013 San Antonio Breast Cancer Symposium showed that Arimidex can lower the risk of first-time, hormone-receptor-positive breast cancer in postmenopausal women at high risk who haven’t been diagnosed. Arimidex isn’t approved by the FDA for this use, but doctors may consider it a good alternative to other hormonal therapies approved to reduce risk in high-risk women.

It’s possible that the FDA may approve Arimidex to be used to reduce risk in high-risk postmenopausal women who haven’t been diagnosed.

Side effects of Arimidex

Because Arimidex lowers the amount of estrogen in the body, less estrogen reaches bone cells, which can lead to bone thinning and weakening and a higher-than-average risk of broken bones. This side effect can be very troubling for some women. If you have osteoporosis, your doctor may recommend that you take tamoxifen rather than Arimidex because of this possible side effect.

Still, the ATAC results reported in 2007 showed a finding that hadn't been seen before. The higher risk of broken bones associated with Arimidex disappeared after the women stopped taking Arimidex. The researchers will see if this result continues as more data is collected and analyzed.

Other common side effects of Arimidex are:

Joint pain from taking Arimidex can be troubling. But a 2008 British study suggests that women who experienced joint pain while taking hormonal therapy medicine were less likely to have the breast cancer come back (recur). Knowing that this side effect might indicate a reduced risk of the cancer coming back may help some women stick with treatment despite the side effects.

Some women may have other side effects while taking Arimidex:

Some side effects may mean that you're having an allergic reaction to Arimidex. If you have any of the following symptoms, call your doctor immediately:

How long do I take Arimidex?

In most cases, you'll take Arimidex for 5 years. Doctors may recommend that some women take it for a longer or shorter period of time.

Does insurance cover Arimidex?

While costs vary, Arimidex can cost several hundred dollars per month. If you have health insurance, check with your insurance company to see if and how much of the cost of Arimidex is covered. If you don't have health insurance or your insurance doesn't cover the cost of Arimidex, ask your doctor or nurse about programs in your area that may be able to help.

AstraZeneca, the company that makes Arimidex, offers the AZ Cancer Support Network, which can help you learn about prescription programs. In the United States, call 1-866-992-9276, or visit the AstraZeneca patient prescription assistance programs page.

You can also read the Paying for Your Care section for information on additional types of financial assistance and cost-lowering tips.

The ATAC study

The ATAC study was the first to report on the use of an aromatase inhibitor in women with early-stage disease. It compared Arimidex and tamoxifen treatment for post-menopausal women with early-stage, hormone-receptor-positive breast cancer. The findings from this study have changed the standard of care for women with early-stage breast cancer. The ATAC study has the longest track record for the results of an aromatase inhibitor – in this case, Arimidex – for use right after surgery. will provide updates on this important study over the coming years.

To connect with others taking Arimidex, visit the Discussion Board thread For Arimidex (Anastrozole) users new, past, and ongoing.

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