120 month follow-up data from the landmark ATAC trial demonstrate that the benefits of anastrozole over tamoxifen start early and continue up to five years after treatment completion in postmenopausal women with hormone receptor-positive early breast cancer.

The new 120 month data from the ATAC (Arimidex, Tamoxifen, Alone or in Combination) trial, one of the world's largest and longest-running studies in postmenopausal women with early breast cancer, was presented at the Milan Breast Cancer Conference, 17th June 2010. It provides further confirmation of the long-term superior efficacy and established safety profile of anastrozole over tamoxifen – even beyond treatment completion.

Breast cancer currently affects approximately 1.1 million women worldwide.2 The long-term risk of early breast cancer returning is significant and this risk remains for up to at least 15 years.3 The goal of early breast cancer treatment is to prevent early and long-term recurrence as, when breast cancer returns and spreads management is likely to be palliative. The new findings from ATAC provide further reassurance that prescribing anastrozole from the start protects women from recurrence throughout the
five year treatment period and up to five years beyond treatment completion (known as the 'carry-over' effect).

The ten year follow-up data found that in hormone receptor-positive patients (n=2618 anastrozole; 2598 tamoxifen) significant improvements were seen for anastrozole compared with tamoxifen for the primary endpoint of Disease Free Survival (DFS) with 735 events (28.1%) seen with anastrozole, compared to 824 events (31.7%) with tamoxifen (HR 0.86; 95% CI 0.78, 0.95).

Similar improvements were seen for Time To Recurrence (TTR) with 456 events (17.4%) seen with anastrozole, compared to 558 events (21.5%) with tamoxifen (HR 0.79; 95% CI 0.70, 0.89). The data also found that numerically death rates after recurrence remained lower on anastrozole compared with tamoxifen, with 284 events (10.8%) vs 320 events (12.3%) respectively (HR 0.87;95% CL 0.74, 1.02).

Professor Jack Cuzick, Head of Department, Cancer Research UK Centre for Epidemiology, Mathematics and Statistics, UK and Lead ATAC trial investigator commented, "The five year 'carry-over' effect of anastrozole demonstrated by the new ATAC data provides further support for prescribing an aromatase inhibitor as initial adjuvant therapy for postmenopausal women with
hormone receptor-positive early breast cancer. No other trial has demonstrated such a clear 'carry-over' effect, and the quality and maturity of the data from the ATAC trial continue to provide confidence for physicians and reassurance to women for using anastrozole in fighting this devastating disease."

The tolerability profile of anastrozole at 120 months was consistent with previous observations from the ATAC trial, with no new safety concerns reported.1 Whilst fracture rates were higher for patients receiving anastrozole compared with tamoxifen during active treatment, following treatment completion rates were similar. The incidence of other new cancers in the anastrozole arm versus the tamoxifen arm was similar overall (425 vs 431), lower with anastrozole for melanoma (8 vs 19), endometrial (6 vs 24) and ovarian (17 vs 28) cancers but continued to be higher with anastrozole for colorectal (66 vs 44) and lung cancer (51 vs 34).

As a result of the proven efficacy and safety evidence for anastrozole, it is now the most widely prescribed AI worldwide, with more than twice as many prescriptions as the next most widely prescribed AI and over 5.5 million patient years' experience.4 These new data provide further evidence that treatment with anastrozole offers postmenopausal women with hormone receptorpositive early breast cancer an improved chance of staying recurrence free for longer compared with tamoxifen.

Source: Astrazeneca Oncology