The Breast Cancer Picture Evolves- Mature ATAC Data

Clinical Professor Alan Coates from the University of Sydney, presented mature data from the ATAC study which compared five years of hormonal therapy with anastrazole or tamoxifen for hormone receptor positive breast cancer.

The study began in July 1986 in 18 countries. Essentially, the study showed anastrazole to be more effective that tamoxifen with a 2.8% absolute benefit at 5 years (recurrence rate for tamoxifen 12.5% vs. 9.7% for anastrazole). This benefit was more obvious at 9 years with an absolute benefit of 4.8% (tamoxifen 21.8% recurrence at 9 years, anastrozole 17%).

The early breast cancer trialists collaborative group (BBCTCG) had previously published in Lancet 2005 defining that there was a statistically significant carry over benefit in favour of anastrazole (50% vs tamoxifen 33% in years 5-9).

The time to distant recurrence was 15.6% at 9 years for tamoxifen and 13.2% for anatrazole. The development of contralateral breast cancer was also reduced at 9 years, 4.2% for tamoxifen, 2.5% for anastrazole.

Professor Coates concluded that at 100 months median follow up, anastrazole was statistically significantly superior to tamoxifen in preventing breast cancer recurrence and that the absolute difference in recurrence rates continues to increase after completion of 5 years treatment.