A lower incidence of gynecologic adverse events and interventions with anastrozole than with tamoxifen in the ATAC trial.

Objective: Results of the Arimidex, Tamoxifen, Alone or in Combination (ATAC) trial have shown that tamoxifen is associated with a significantly higher incidence of gynecologic adverse events than anastrozole.

Study Design: This was a retrospective analysis of all gynecologic adverse events and interventions conducted in patients receiving anastrozole or tamoxifen in the main ATAC trial database.

Results: Women taking tamoxifen experienced significantly more gynecologic adverse events than those taking anastrozole (34.2% vs 20.5%; P < .0001) and this led to more diagnostic and/or therapeutic interventions, including an almost 4-fold increase in the number of hysterectomies (5.1% vs 1.3%; P < .0001). The majority of the gynecologic adverse events with tamoxifen occurred during the first 2.5 years.

Conclusion: The lower incidence of gynecologic adverse events and interventions with anastrozole and the early occurrence of these events provide further support for using anastrozole as the initial adjuvant treatment for early hormone receptor-positive breast cancer.