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.