The ATAC (Arimidex, Tamoxifen, Alone or in Combination) adjuvant breast cancer trial in postmenopausal (PM) women.

Abstract

The ATAC trial evaluates, in a randomized double-blind design, ‘Arimidex’ (anastrozole), alone or in combination with tamoxifen, relative to tamoxifen alone as 5-year adjuvant treatment for PM women with early breast cancer (EBC). Methods: Patients with operable invasive breast cancer who had completed primary treatment and were candidates to receive adjuvant hormonal therapy were randomized. Radiotherapy could be administered together with trial treatment. The main endpoints are recurrence-free survival and tolerability. Other endpoints are time to distant metastasis, overall survival and incidence of new breast primaries. Four subprotocols were also conducted: quality of life (QoL), effect on bone and endometrium, and pharmacokinetics (PK). The main trial analysis was pre-determined to take place after 1056 events had occurred. Results: In approximately 30 months, the trial recruited 9366 patients from 380 centres in 21 countries. Of these, 1105, 307, 285 and 357 were included in the QoL, bone, endometrial and PK subprotocols, respectively. The median age was 63 years with 65% 60 years. Mastectomy was performed in 48% of the patients and 95% of the patients had axillary surgery (62% clearance and 33% sampling). The median number of axillary nodes examined was 14 among patients who had an axillary clearance and nine among those who had a sampling surgical procedure. 61% of patients were node negative and 64% of all patients had tumours 2cm. 74% of patients were oestrogen receptor (ER) and/or progesterone receptor (PR) positive; the tumour blocks for receptor-unknown patients are currently being analysed for ER and PR status. 68% of tumours were well or moderately differentiated. 21% of patients received chemotherapy prior to randomization and 63% received radiotherapy. One interim analysis, pre-defined in the protocol, was performed by the independent statistician and the results reviewed by the Independent Data Monitoring Committee which recommended the trial continue unchanged. Conclusion: The ATAC trial is the single largest adjuvant trial ever conducted in PM patients with EBC. Data from the trial will be presented.