Anastrozole Superior to Tamoxifen as Adjuvant Treatment in Early Breast Cancer

Laurie Barclay, MD

December 13, 2002

Dec. 13, 2002 — Anastrozole (Arimidex) is clearly superior to tamoxifen as adjuvant treatment for women with early-stage breast cancer, according to the results of a randomized, double-blind trial presented on Dec. 13 at the San Antonio Breast Cancer Symposium.

"Anastrozole showed superior efficacy to tamoxifen for disease-free survival, time to recurrence, and the incidence of contralateral breast cancer," write R. Bianco, from the Università di Napoli Federico II in Italy, and colleagues from the ATAC Trialists' Group. "The benefits seen with anastrozole are attributed to improved drug activity rather than a sub-optimal effect of tamoxifen. These results show anastrozole to be a highly effective treatment option for postmenopausal patients with early breast cancer."

The ATAC trial randomized 9,366 postmenopausal patients with operable early breast cancer following surgery with or without chemotherapy and/or radiotherapy to adjuvant treatment with tamoxifen, 20 mg; anastrozole, 1 mg; or the combination of both drugs. Estrogen and/or progesterone receptors were positive in 84% of patients. Median duration of therapy was 30.7 months, and median follow-up was 33.3 months.

Compared with tamoxifen, there were improvements with anastrozole in disease-free survival (hazard ratio [HR], 0.83; 95% confidence interval [CI], 0.71 - 0.96; P = .013), time to recurrence (HR, 0.79; 95% CI, 0.67 - 0.94; P = .008), and incidence of contralateral breast cancer (P = .007). Starting from year two, annual breast cancer event rates began to be lower in the anastrozole and combination groups than in the tamoxifen group.

Improvements were similar in the subgroup of patients with estrogen and/or progesterone-receptor positive tumors. There were distant recurrences in 180 patients receiving anastrozole, 203 receiving tamoxifen, and 232 receiving the combination.

"For the first time there is a choice of adjuvant endocrine therapy for [postmenopausal] women with hormone responsive tumors," the authors write. "Longer follow-up will enable a more mature benefit/risk assessment to be made."

Funding for the study was provided by AstraZeneca, which makes both anastrozole and tamoxifen.

25th Annual SABCS: Abstract 632. Presented Dec. 13, 2002.

Reviewed by Gary D. Vogin, MD

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