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Arimidex May Be More Successful Than Tamoxifen in Post-Menopausal Breast Cancer Patients (dateline December 30, 1999)


A large study presented at the 22nd Annual San Antonio Breast Cancer Symposium revealed that post-menopausal women with advanced breast cancer may benefit more from treatment with the drug Arimidex (generic name anastrozole) than with the commonly prescribed drug, tamoxifen (trade name Nolvadex). The study combined data from two research groups: the North American research group and the European group, TARGET (Tamoxifen and Arimidex Randomized Group Efficacy and Tolerability). Women treated with tamoxifen were found to have a 13% higher risk of disease progression than those treated with Arimidex.

The randomized, double-blind study included 1021 post-menopausal women with Stage IV breast cancer (also called metastatic cancer). Metastatic breast cancer has spread past the breast and underarm lymph nodes to other areas of the body such as the bone, lung, liver, or brain. The study marks the first time researchers have directly compared the effects of tamoxifen and Arimidex in a clinical trial according to Professor Aman Buzdar of the University of Texas’ M.D. Anderson Cancer Center. Arimidex was approved by the U.S. Food and Drug Administration (FDA) in January 1996 as treatment for post-menopausal women with metastatic breast cancer who have not responded well to treatment with tamoxifen.

Researchers are surprised at the results of the Arimidex study since tamoxifen and Arimidex fight breast cancer in distinctly different ways. While tamoxifen blocks estrogen receptors in breast cancer cells, Arimidex works by interfering with the body’s ability to synthesize estrogen. Arimidex is a non-steroid compound known as a selective aromatase inhibitor. Since Arimidex inhibits the body’s conversion of certain steroid hormones (androgens) to estrogen by the enzyme aromatase, Arimidex decreases the overall concentration of estrogen, thus reducing the spread of breast cancer in post-menopausal women. Since androgens also act as weak estrogens and participate in the overall production of estrogen, women who produce adequate levels of androgens often do not need to use hormone replacement therapy to prevent menopausal symptoms and osteoporosis.

A long-term study comparing Arimidex with tamoxifen in early-stage breast cancer patients is currently underway. ATAC (Arimidex, Tamoxifen Alone or in Combination) is the largest study of hormonal treatment ever undertaken and involves over 9,000 post-menopausal women from cancer centers worldwide. In addition to evaluating the safety of the two drugs, researchers will also investigate whether a combined treatment of Arimidex and tamoxifen improves patient outcomes. Results of the ATAC study are due in 2001.

Most post-menopausal women treated with Arimidex take one 1-mg tablet each day. Arimidex cannot distinguish between normal cells and cancer cells, and consequently, may cause some side effects. The most common side effects to treatment include a general feeling of weakness and a decreased energy level. Other less common side effects include:

  • Headache
  • Nausea
  • Mild diarrhea
  • Increased or decreased appetite
  • Sweating
  • Hot flashes
  • Vaginal dryness
  • Temporary hair thinning

Rare side effects of Arimidex include blood clots with redness or mild swelling of arms, legs and ankles, pain in leg calves, shortness of breath, or difficulty breathing. Not all women with advanced breast cancer are candidates for Arimidex therapy. Because Arimidex decreases the body’s overall estrogen level, women at high risk of osteoporosis may not be suited for Arimidex therapy. Post-menopausal women are encouraged to discuss Arimidex with their physician or cancer treatment team.

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