Commenting on these highly important results, Bernard Tyrrell, Vice President, Oncology Therapy Area, AstraZeneca, said, “These updated results are extremely exciting and confirm that our initial optimism, expressed at the time of the main analysis, was justified. ARIMIDEX represents new hope for postmenopausal women with early breast cancer”.

Arimidex 2002 sales year-to-date through October were $283 million, an 81% increase over the same period last year. The early breast cancer market could be worth approximately $2 billion.

ATAC is the largest breast cancer trial ever performed, involving over 9,300 patients. The protocol-defined major analysis of the trial with a median follow-up of 33 months – presented at the corresponding meeting last year – has already shown superior efficacy of ARIMIDEX versus tamoxifen for disease free survival (DFS), time to a recurrence (TTR), and incidence of contralateral breast cancer. A number of important tolerability benefits were also identified. These latest results are from the first and only efficacy update performed since that time.

The median follow-up in the ATAC trial now extends to almost 4 years. ARIMIDEX continues to show statistically significant benefits over tamoxifen in all efficacy endpoints studied for the clinically relevant population of patients with hormone receptor-positive tumours, a group which represents about two-thirds of the general postmenopausal breast cancer population overall. The updated analysis shows a 14 per cent reduction in the risk of recurrence (DFS) among patients treated with ARIMIDEX compared with tamoxifen (p=0.030). Among women with hormone-sensitive tumours who represent 84 per cent of patients in the trial, and are the target population for this therapy - this risk reduction is even greater at 18 per cent (p=0.014).

Importantly, the absolute difference between the two treatments continues to increase - the absolute difference in DFS rates has increased from 2.0 per cent at 3 years (at the time of the major analysis) to 2.4 per cent at 4 years. In the clinically relevant hormone-receptor positive population, this absolute difference is even greater at 2.9 per cent. At the time of this updated analysis, 46 per cent of patients have completed more than 4 year’s follow-up.

Additionally, a separate safety update also presented at this year’s meeting, which provides an extra 7 months’ data over the major analysis, confirms the initial favourable tolerability profile of Arimidex over tamoxifen. No new safety issues have emerged.

ARIMIDEX, as the first and only drug to have shown significant efficacy and tolerability benefits over tamoxifen in postmenopausal women with early breast cancer, is now the only other hormonal drug approved for this use. Approvals have already been granted in several major markets including the USA, UK and Japan. With over 650,000 patient years of experience, ARIMIDEX is the most widely used aromatase inhibitor in the world.