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October 22, 2001

Experts Confirm 'Arimidex' (anastrozole) as a Gold Standard for Advanced Breast Cancer

New publication confirms the superiority of 'Arimidex' over tamoxifen in the first-line treatment of hormone-sensitive breast cancer

 (SafetyAlerts) -  'Arimidex' (anastrozole) should now replace tamoxifen as a first choice, first-line therapy for post-menopausal women with hormone- sensitive* advanced breast cancer, according to the full results of a study involving the largest patient population ever investigated comparing these two treatments in the advanced setting, published in the peer-review journal Cancer** today.

The study programme involved two randomised, double blind multicentre trials,*** one conducted in North America and Canada and the second conducted in the rest of the world, which compared daily treatment with 'Arimidex' 1mg or tamoxifen 20mg in post-menopausal women with hormone-sensitive or receptor unknown tumours. The data published today are the full analysis of the combined results of these two studies, which between them, involved over 1,000 breast cancer patients.

The results in patients who had confirmed hormone-sensitive tumours (60% of the study population and the target patients for this intervention), were very encouraging. A retrospective analysis of this patient subgroup revealed that 'Arimidex' was significantly superior to tamoxifen in terms of median time to disease progression (TTP) (median 10.7 months vs 6.4 months respectively, 2P=0.022).

The investigators explored a number of possible prognostic factors which could have contributed to the superior efficacy seen with 'Arimidex' in these patients (age, prior treatment, presence/absence of visceral, liver or bone metastases) and concluded that only the hormone receptor status of the tumour had any significant impact on treatment difference. In light of this finding, the investigators believe that the benefits of 'Arimidex' over tamoxifen may have been diluted in the results from the overall population by the high proportion of patients with tumours of 'unknown' hormone receptor status included in the combined analysis (40%). The differing mechanisms of action of the two compounds could hold the key to the superiority of the 'Arimidex' treatment.

The potential impact of these differences in terms of treatment side effects were also explored in the combined analysis. Both compounds were generally well tolerated and appeared similar in terms of number of side effects reported. However, a significantly lower incidence of thromboembolic events were observed in patients receiving 'Arimidex' compared with those who received tamoxifen (3.6% vs 6.5% respectively; p=0.0434, not adjusted for multiple analysis). In addition, only 1.0% of patients taking 'Arimidex' reported vaginal bleeding - a psychologically distressing side effect which adversely affects quality of life - when compared with 2.2% in the tamoxifen group. Reassuringly, given the potency of 'Arimidex' in suppressing oestrogen synthesis, an effect which in theory might have an unfavourable impact on bone metabolism, there was no difference between the treatment groups in terms of bone fractures.

Reviewing these exciting new findings, the authors concluded, "In post- menopausal women with hormonally-sensitive breast cancer, anastrozole should be considered as the new standard first-line treatment."

Lead investigator Professor Jacques Bonneterre, Professor of Medical Oncology, Centre Oscar Lambret, France, says, "The optimum balance of the efficacy and tolerability data confirm that 'Arimidex' should be considered as a new standard first-line treatment for post-menopausal women with hormonally- sensitive breast cancer. 'Arimidex' was shown to be more efficacious than tamoxifen in patients with hormone-sensitive disease, who are the most appropriate group of patients for hormonal therapy in advanced breast cancer. The data also showed 'Arimidex' to be at least as well tolerated as tamoxifen , with a lower incidence of thromboembolic events. Furthermore, the low incidence of vaginal bleeding observed with 'Arimidex' provides indirect evidence of its lack of stimulatory effect on the endometrium."

Because 'Arimidex' is potent and is the most selective 1, 2,3, 4 aromatase inhibitor in the clinical setting, it provides near maximal oestrogen suppression and is also well tolerated, while tamoxifen acts as a partial agonist at oestrogen receptors in the breast tumour cell. The profound reduction in circulating oestrogen levels which are achieved with 'Arimidex' could be a more effective method of halting tumour cell proliferation than partial oestrogen receptor inhibition. The next step will be to establish if the proven clinical benefits of 'Arimidex' in advanced disease translate into the early breast cancer setting, which will be revealed later this year when results from the ATAC ('Arimidex', Tamoxifen, Alone or in Combination) Study, involving over 9,000 patients, become available.

'Arimidex' is a trademark, the property of the AstraZeneca group of companies.

* In these studies, hormone-sensitive refers to ER+ve and/or PR+ve tumours
** Bonneterre J, Buzdar A, Nabholtz JM, et al. Anastrozole (Arimidex) is
Superior to Tamoxifen as First-line Therapy in Hormone Receptor-positive
Advanced Breast Cancer: Results of Two Randomized Trials Designed for
Combined Analysis. Cancer, 2001
*** The North American study was conducted in 97 centres across the US and
Canada. The Rest of World study was conducted in 83 sites in Europe,
Australia, New Zealand, South America and South Africa. These studies have
been individually reported in the Journal of Clinical Oncology (Nov 2000, 18
(22) 3748-3767)

Notes to Editors

'Arimidex' is a potent, highly selective, non-steroidal aromatase inhibitor that exerts a therapeutic effect by inhibiting a key step in the production of oestrogen: 'Arimidex' inhibits the conversion of androgens to oestrogens by the enzyme aromatase. In this way, 'Arimidex' suppresses the levels of oestrogen circulating in the blood to non-detectable levels in post-menopausal women.
'Arimidex' is currently approved for the first-line treatment of advanced breast cancer in postmenopausal women in 24 markets, the US, UK, Italy, France, Germany, Canada, Spain, Austria, Belgium, Brazil, Denmark, Finland, Ireland, Luxembourg, Mexico, Netherlands, New Zealand, S. Africa, Slovakia, Czech Republic, Malta, Norway, Australia and Switzerland.
'Arimidex' is also available in most countries for the treatment of advanced breast cancer in postmenopausal women whose disease has progressed following treatment with tamoxifen or other anti-oestrogens.
'Arimidex' is the most widely used aromatase inhibitor currently with over 430,000 patient years experience.

Source: PRNewswire.

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