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'Arimidex' (anastrozole) significantly reduces the risk of contralateral breast tumours compared to gold-standard tamoxifen

March 21, 2002

Latest results from the ATAC (Arimidex, Tamoxifen Alone or in Combination) study in early breast cancer, presented today at the 3rd European Breast Cancer Conference (EBCC), show that treatment with 'Arimidex' more than halved the risk of post-menopausal women developing new tumours in the other previously healthy (contralateral) breast compared with tamoxifen.

Patients in the 'Arimidex` treatment arm had a 58% lower risk of developing a contralateral breast tumour compared with those taking tamoxifen (OR=0.42, p=0.0068). Furthermore, in postmenopausal women with receptor-positive* breast tumours, `Arimidex` was shown to lower the risk of contralateral breast cancer by 64% compared with tamoxifen (OR=0.36, p=0.0040).

"The contralateral tumour data for 'Arimidex' are exceptional" commented Dr Jeffrey Tobias, ATAC investigator and consultant oncologist at University College Hospital, London, UK, speaking today from the EBBC. "We know that women successfully treated for early breast cancer still have a 3-fold increased risk of developing a new tumour in the opposite breast compared with women who have not had breast cancer. Tamoxifen therapy reduces this risk by nearly a half. To find a treatment that cuts this risk in half again is truly remarkable - and welcome news for the millions of postmenopausal women diagnosed with early breast cancer every year." he continued.

At the time of data cut-off in the ATAC Trial (median treatment duration of 30.7 months and median follow-up of 33.3 months), there were 9 cases of invasive and 5 cases of DCIS stage contralateral breast cancer among 3,125 `Arimidex` patients, compared with 30 cases of invasive and 3 cases of DCIS stage contralateral breast cancer in 3,116 tamoxifen patients (0.4% `Arimidex` vs. 1.1% tamoxifen; Odds Ratio=0.42 95% CI 0.22-0.79; p=0.0068).

The benefits of 'Arimidex' over tamoxifen seen in the ATAC trial were not confined to a reduction in the incidence of new (contralateral) breast primaries. The first presentation of the ATAC study at the 23rd Annual San Antonio Breast Cancer Symposium in December 2001 clearly demonstrated that 'Arimidex' is significantly more effective than tamoxifen in terms of improving disease-free survival in this patient population, and that it also has a number of important tolerability benefits over the current gold standard.
These include a significant reduction in the incidence of endometrial cancer, vaginal bleeding, venous thromboembolic events (including DVTs) and hot flushes. As expected, tamoxifen was associated with a lower risk of musculo-skeletal disorders and fractures common to this age group of women compared with `Arimidex`.

The 'Arimidex'/tamoxifen combination showed no additional efficacy or tolerability benefits compared with tamoxifen alone. There were no safety issues associated with the combination treatment.

The results seen with tamoxifen in the ATAC trial were as expected, and in line with previous experience as demonstrated by the Early Breast Cancer Trialists' Collaborative Group (EBCTCG) World Overviews of adjuvant tamoxifen therapy1. This would strongly support the conclusion that the beneficial results seen with `Arimidex` in this extensive trial are due to the superior activity of 'Arimidex', rather than inferior efficacy of tamoxifen.

This is the first time ever that another treatment has been proven in a large-scale clinical trial to be superior to tamoxifen in postmenopausal women with early breast cancer, and it marks an incredibly important breakthrough in the management of this devastating disease. ATAC is the largest cancer trial ever conducted, involving over 9,300 post-menopausal women world-wide.


Further data from an independent Spanish trial also presented at EBCC show a significant survival advantage for `Arimidex` over tamoxifen in the advanced breast cancer setting - the first time any survival benefit has been shown over tamoxifen in patients with advanced disease

Lead investigator, Professor Alfredo Milla-Santos of the Medical Oncology Service, Sanitas Hospitales, Barcelona, presented results from his study of 238 postmenopausal women with hormone-sensitive advanced breast cancer treated with either Arimidex (1mg daily, n=121) or tamoxifen (40mg daily, n=117). After a median follow-up of 13.3 months, 40% of patients in the `Arimidex` group had survived, compared with just 11% in the tamoxifen group. Furthermore, median duration of survival was significantly longer for 'Arimidex' than for tamoxifen at 17.4 months vs. 16.0 months (HR=0.64 [95% CI 0.47-0.86, p=0.003). The time to progression (TTP) in patients achieving clinical benefit was 18 months for the 'Arimidex' group, compared with just 7 months for tamoxifen (p<0.01). Both treatments were well tolerated. Professor Milla-Santos concluded by saying that these important results further support the use of ‘Arimidex’ as first line treatment for patients with hormone-sensitive advanced breast cancer.

*Tumours known to be oestrogen receptor (ER) and/or progesterone receptor (PR) positive

‘Arimidex’ is a trademark, property of the AstraZeneca Group of Companies.

Definitions:
OR = Odds Ratio
Clinical Benefit = complete response (CR) + partial response (PR) + stable disease (SD) > 24 weeks.

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