The Arimidex, Tamoxifen, Alone or in Combination (ATAC) Trial

• The Arimidex, Tamoxifen, Alone or in Combination (ATAC) trial:
  • Was the first study to compare:
    • A 3rd-generation aromatase inhibitor (AI), anastrozole, with tamoxifen for the adjuvant treatment of early breast cancer
• The ATAC trial:
  • As designed to compare the efficacy and safety of:
    • Anastrozole (1 mg) with tamoxifen (20 mg) as adjuvant treatment for postmenopausal women with early-stage breast cancer
  • Patients were treated every day for 5 years
  • The study was a double-blind, prospective, randomized trial:
    • With 9,366 postmenopausal women
  • A proportional hazards model was used to assess:
    • The primary endpoints of:
      • DFS
    • Secondary endpoints of:
      • Time to recurrence
      • Time to distant recurrence
      • Overall survival
      • Death with or without recurrence
  • The combination arm of anastrozole and tamoxifen:
    • Was discontinued after the initial analysis:
      • As it was found to have no efficacy or tolerability benefits over tamoxifen alone.
  • Long-term follow-up of 120 months showed:
    • Significant improvements in the anastrozole group versus the tamoxifen group for:
      • DFS, time to recurrence, and time to distant recurrence
    • In hormone receptor-positive patients:
      • These benefits were seen to increase over time
    • Recurrence rates were found to:
      • Remain lower on anastrozole after treatment was completed
    • There was little difference in overall survival:
      • Between anastrazole and tamoxifen (hazard ratio, 0.95; 95% confidence interval, 0.84–1.06; P=0.4)
    • Fractures were more frequent during the active treatment in patients receiving anastrozole:
      • But were similar between the two groups in post-treatment follow-up
    • Treatment-related serious adverse events:
      • Were less common in the anastrozole group:
        • But were also found to be similar between the two groups after treatment completion
      • Anastrozole showed a non-significant increased incidence of colorectal cancer and lung cancers, and a decreased incidence of endometrial, melanoma, and ovarian cancers:
        • However, only the decrease in endometrial cancers remained statistically significant after Bonferroni correction (P<0.001)
    • Overall, anastrozole was found to have:
      • Superior long-term efficacy and safety than tamoxifen as initial adjuvant therapy for postmenopausal women with hormone-sensitive early-stage breast cancer
      • Outcomes from the ATAC trial made anastrozole the preferred treatment for postmenopausal women with localized hormone receptor-positive breast cancer
• References
  • Howell A, Cuzick J, Baum M, Buzdar A, Dowsett M, Forbes JF, et al. Results of the ATAC (arimidex, tamoxifen, alone or in combination) trial after completion of 5 years’ adjuvant treatment for breast cancer. Lancet. 2005;365(9453):60-62.
  • Cuzick J, Sestak I, Baum M, Buzdar A, Howell A, Dowsett M, et al; ATAC/LATTE Investigators. Effect of anastrozole and tamoxifen as adjuvant treatment for early-stage breast cancer: 10-year analysis of the ATAC trial. Lancet Oncol. 2010;11(12):1135-1141.

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