ATAC Trial

  • The Arimidex, Tamoxifen, Alone or in Combination trial (ATAC):
    • Was 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
      • 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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