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

• The ATAC trial:
  • 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 9366 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:
    • 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
    • Lung cancers
  • Decreased incidence of:
    • Endometrial
    • Melanoma
    • 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

1. Cuzick J, Sestak I, Baum 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;11:1135-1141.
2. Howell A, Cuzick J, Baum M, 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;365:60-62.

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