Extended adjuvant therapy with anastrozole among postmenopausal breast cancer patients: results from the randomized Austrian Breast and Colorectal Cancer Study Group Trial 6a

J Natl Cancer Inst. 2007 Dec 19;99(24):1845-53. doi: 10.1093/jnci/djm246. Epub 2007 Dec 11.


Background: Clinical trial data have shown that among breast cancer patients who were disease free after 5 years of adjuvant treatment with tamoxifen, further extended treatment with the nonsteroidal aromatase inhibitor letrozole reduces breast cancer recurrence. We examined the efficacy and tolerability of extended adjuvant therapy with another aromatase inhibitor, anastrozole, for 3 years among women who had completed 5 years of adjuvant therapy.

Methods: Austrian Breast and Colorectal Cancer Study Group (ABCSG) Trial 6a is an extension of ABCSG Trial 6, in which hormone receptor-positive postmenopausal patients received 5 years of adjuvant tamoxifen, with or without the aromatase inhibitor aminoglutethimide, for the first 2 years of therapy. For ABCSG Trial 6a, patients who were disease free at the end of Trial 6 were randomly assigned to receive either 3 years of anastrozole or no further treatment. Efficacy data were analyzed with the use of a Cox proportional hazards regression model with two-sided P values and Kaplan-Meier curves, and tolerability data were estimated using logistic regression analysis with odds ratios and 95% confidence intervals (CIs).

Results: ABCSG Trial 6a included 856 patients. At a median follow-up of 62.3 months, women who received anastrozole (n = 387) had a statistically significantly reduced risk of recurrence (locoregional recurrence, contralateral breast cancer, or distant metastasis) compared with women who received no further treatment (n = 469; hazard ratio = 0.62; 95% CI = 0.40 to 0.96, P = .031). Anastrozole was well tolerated, and no unexpected adverse events were reported.

Conclusions: These data confirm the benefit of extending adjuvant tamoxifen therapy beyond 5 years with anastrozole compared with no further treatment. Further research is required to define the optimum length of extended adjuvant therapy and to investigate the possibility of tailoring this period to suit different disease types.

Publication types

  • Multicenter Study
  • Randomized Controlled Trial
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aged
  • Aged, 80 and over
  • Aminoglutethimide / therapeutic use
  • Anastrozole
  • Antineoplastic Agents, Hormonal / administration & dosage
  • Antineoplastic Agents, Hormonal / adverse effects
  • Antineoplastic Agents, Hormonal / therapeutic use*
  • Aromatase Inhibitors / administration & dosage
  • Aromatase Inhibitors / adverse effects
  • Aromatase Inhibitors / therapeutic use*
  • Austria
  • Breast Neoplasms / chemistry
  • Breast Neoplasms / drug therapy*
  • Breast Neoplasms / pathology
  • Breast Neoplasms / prevention & control
  • Breast Neoplasms / surgery
  • Chemotherapy, Adjuvant
  • Disease-Free Survival
  • Drug Administration Schedule
  • Female
  • Humans
  • Kaplan-Meier Estimate
  • Logistic Models
  • Lymphatic Metastasis
  • Male
  • Middle Aged
  • Nitriles / administration & dosage
  • Nitriles / adverse effects
  • Nitriles / therapeutic use*
  • Odds Ratio
  • Postmenopause*
  • Proportional Hazards Models
  • Prospective Studies
  • Receptors, Estrogen / analysis
  • Receptors, Progesterone / analysis
  • Research Design
  • Tamoxifen / therapeutic use
  • Treatment Outcome
  • Triazoles / administration & dosage
  • Triazoles / adverse effects
  • Triazoles / therapeutic use*


  • Antineoplastic Agents, Hormonal
  • Aromatase Inhibitors
  • Nitriles
  • Receptors, Estrogen
  • Receptors, Progesterone
  • Triazoles
  • Tamoxifen
  • Aminoglutethimide
  • Anastrozole