Commentary

The primary rationale for utilizing tamoxifen in high-risk women in clinical trials, such as NSABP P-1, was the reduction in contralateral breast cancer observed with adjuvant tamoxifen in patients with invasive breast cancer. The preliminary results of the ATAC trial demonstrated 56% fewer second breast cancers in women randomized to anastrozole compared to tamoxifen. Based on these early findings, most surgeons surveyed believe that a randomized trial comparing anastrozole to tamoxifen in high-risk postmenopausal women would demonstrate both greater efficacy and less toxicity for anastrozole. Sixty percent of surgeons would use anastrozole in these women at the present time, for which there is no FDA indication, but breast cancer researchers almost uniformly believe that aromatase inhibitors should only be utilized in high-risk patients as part of a clinical trial. In the United Kingdom, a massive trial is being planned to evaluate the use of anastrozole in high-risk patients. The final design of this IBIS II trial is awaiting the presentation of IBIS I study results comparing tamoxifen to placebo.

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