Impact of the ATAC trial on prescribing of hormonal therapy in breast cancer

Abstract

11028 Background: The arimidex, tamoxifen, alone or in combination (ATAC) trial recommended use of anastrazole over tamoxifen as initial adjuvant hormonal therapy of early breast cancer in postmenopausal women. The aim of this study was to investigate the impact of the publication of the ATAC trial in December 2004 on subsequent prescribing of hormonal therapy to Irish women =55 years old. Methods: The Irish HSE-PCRS pharmacy claims database was used to identify all women =55 years old, commenced on tamoxifen or an aromatase inhibitor as initial hormonal therapy, between July 2000 and June 2006. A segmented regression analysis of an interrupted time series was used to detect changes in the trend and level of anastrazole prescribing after publication of the ATAC trial in December 2004 and the prior updates in November 2003 and June 2002 (presented December 2001). β coefficients and 95%CI are presented where appropriate. The absolute change in anastrazole prescribing and 95%CI are also calculated for selected months. Statistical analysis was performed using SAS version 9.1. Significance at p<0.05 is assumed. Results: A cohort of 7,604 women =55 years old, commenced on initial hormonal therapy, was identified from the HSE-PCRS database, 2,206 (29%) of these women were prescribed anastrazole. In the month following publication of the final results of the ATAC trial there was a 17.6% (95% CI 10.8%, 24.5%) absolute increase in anastrazole prescribing. This represented a statistically significant increase in the level of prescribing (level change β=18.1 95% CI 11.3, 24.9 p<0.0001). There was also a significant change in anastrazole prescribing trend after presentation of the first ATAC update (slope change β=0.98 95% CI 0.59, 1.37 p<0.0001). Conclusion: The publication of the final ATAC trial data resulted in a significant increase in the prescribing of anastrazole. This is objective evidence that oncologists respond rapidly to clinical trial results. It is unclear whether the significant increase in anastrazole prescribing after the first ATAC update is an appropriate response to an interim analysis. No significant financial relationships to disclose.