According to results recently published in the Lancet, long-term (100-month) follow-up data demonstrates that postmenopausal women with hormone-positive breast cancer have a significantly reduced risk of developing a cancer recurrence when they are initially treated with Arimidex® (anastrozole) compared with initial treatment with tamoxifen (Nolvadex®). These results were also recently presented at the 2007 annual San Antonio Breast Cancer Symposium.
Each year breast cancer is diagnosed in over 178,000 women in the United States alone. Many of these breast cancers will be hormone receptor-positive, meaning that they are stimulated to grow by the circulating female hormones estrogen and/or progesterone.
Treatment of hormone receptor-positive breast cancer often involves hormonal therapies that suppress or block the action of estrogen. These therapies include tamoxifen as well as agents known as aromatase inhibitors. Tamoxifen acts by blocking estrogen receptors, whereas aromatase inhibitors suppress the production of estrogen in postmenopausal women.
To determine how best to use aromatase inhibitors in the treatment of postmenopausal breast cancer, researchers have considered these possibilities:
- Use of aromatase inhibitors as extended hormonal therapy, after a woman has completed tamoxifen treatment
- Switching to aromatase inhibitors after a brief (two- to three-year) period of tamoxifen therapy
- Use of aromatase inhibitors in place of tamoxifen as initial hormone therapy
While it’s still uncertain which of these approaches is best, each of them appears to produce better outcomes than use of tamoxifen alone. The primary benefit observed thus far with use of aromatase inhibitors is a reduction in the risk of cancer recurrence.
The ATAC (Arimidex, Tamoxifen, Alone or in Combination) Study was designed to compare use of the aromatase inhibitor Arimidex with tamoxifen as initial hormonal therapy in postmenopausal women with early breast cancer. Study participants in both groups received five years of hormonal therapy. Median follow-up is now more than eight years.
- Women treated with Arimidex continue to experience a lower risk of breast cancer recurrence, including a lower risk of distant recurrence, than women treated with tamoxifen.
- Women treated with Arimidex were less likely to develop cancer in the opposite breast than women treated with tamoxifen.
- There is still no difference in overall survival between the two study groups.
- Although women treated with Arimidex were more likely than women treated with tamoxifen to develop a bone fracture during treatment, fracture risk was similar in the two groups during the years following treatment.
These results indicate that, even with longer follow-up, postmenopausal breast cancer patients who were treated with Arimidex have a lower risk of cancer recurrence than patients who were treated with tamoxifen.
 The Arimidex, Tamoxifen, Alone or in Combination (ATAC) Trialists’ Group. Effect of anastrozole and tamoxifen as adjuvant treatment for early-stage breast cancer: 100-month analysis of the ATAC trial. Lancet. 2008;9:45-53.
 Forbes JF, Cuzick J, Buzdar A et al. ATAC: 100-months median follow-up (FU) shows continued superior efficacy with no excess fracture risk for anastrozole (A) compared with tamoxifen (T) after treatment completion. Presented at the 30th Annual San Antonio Breast Cancer Symposium. San Antonio, TX, December 13-16, 2007. Abstract #41.