Anastrozole alone or in combination with tamoxifen versus tamoxifen alone for adjuvant treatment of postmenopausal women with early breast cancer: first results of the ATAC randomised trial
- Study type
- Clinical trial
- Study name
- ATAC
- Design
- Randomised trial with three treatment arms; efficacy analysis by intention to treat
- Sample size
- 9366 patients
- Source
- The Lancet · 2002
In plain words
In this large study, postmenopausal women with early breast cancer, after their first treatment, took anastrozole, tamoxifen or a combination of the two for 5 years. In patients whose cancer was hormone receptor positive, anastrozole was slightly better than tamoxifen at preventing the cancer from coming back, and combining the two medicines gave no more benefit than tamoxifen alone. Anastrozole caused fewer side effects such as vaginal bleeding, blood clots in the veins and hot flushes, but pain and muscle and joint problems and broken bones were more common with it. The choice of medicine should be made with the treating doctor and based on each patient's circumstances.
Key results
Treatment arms and regimens
3125 patients; treatment for 5 years.
Anastrozole 1 mg orally daily for 5 years or until recurrence.
3116 patients; treatment for 5 years.
Tamoxifen 20 mg orally daily for 5 years or until recurrence.
3125 patients; treatment for 5 years.
Anastrozole 1 mg + tamoxifen 20 mg orally daily for 5 years or until recurrence.
Source of the regimen details: FDA label for Arimidex (DailyMed, section 14.1, ATAC) and abstract of the paper
Doses are given for the information of specialists, as in this study’s protocol, and are not a prescription. Every drug must be prescribed by the treating physician for the individual patient.
Study population
Postmenopausal women with operable invasive breast cancer who had completed primary treatment and were candidates for adjuvant hormonal therapy. Hormone receptor status was reported as positive in 7839 patients (84%).
Endpoints
Primary endpoints: disease-free survival and occurrence of adverse events. The efficacy analysis was by intention to treat.
Safety and side effects
Anastrozole was significantly better tolerated than tamoxifen with respect to endometrial cancer (P=0.02), vaginal bleeding and discharge (both P<0.0001), cerebrovascular events (P=0.0006), venous thromboembolic events (P=0.0006) and hot flushes (P<0.0001). Tamoxifen was significantly better tolerated than anastrozole with respect to musculoskeletal disorders and fractures (both P<0.0001). Rates of grade 3 or higher adverse events are not reported in the abstract.
Clinical significance and place in guidelines
On the basis of this first analysis, anastrozole is an effective and well-tolerated option for adjuvant hormonal therapy in postmenopausal women with hormone-sensitive early breast cancer, and its combination with tamoxifen showed no advantage over tamoxifen alone. The authors stressed that longer follow-up is needed for a final assessment of benefit versus risk. The current status in clinical guidelines and drug approvals should be checked separately and is not mentioned in the abstract.
Limitations
This paper reports the first results with a short median follow-up (33.3 months), and the authors themselves consider longer follow-up necessary for a final assessment of benefit and risk. The effect of anastrozole was seen only in the hormone receptor-positive subgroup. Patients with hormone receptor-negative or unknown status were also part of the study population. An erratum to this paper was published in the same journal.
This summary was prepared by the editorial team from the published paper; the original paper is the final reference. Read the original abstract on PubMed.