Switching of postmenopausal women with endocrine-responsive early breast cancer to anastrozole after 2 years' adjuvant tamoxifen: combined results of ABCSG trial 8 and ARNO 95 trial

Lancet. 2005 Aug 6-12;366(9484):455-62. doi: 10.1016/S0140-6736(05)67059-6.

Abstract

Background: Tamoxifen has been the standard adjuvant treatment for postmenopausal women with hormone-responsive early breast cancer for more than 20 years. However, the third-generation aromatase inhibitor anastrozole has proven efficacy and tolerability benefits compared with tamoxifen when used as initial adjuvant therapy. We investigate whether women who have received a period of adjuvant tamoxifen would benefit from being switched to anastrozole.

Methods: We present a combined analysis of data from two prospective, multicentre, randomised, open-label trials with nearly identical inclusion criteria. Postmenopausal women with hormone-sensitive early breast cancer who had completed 2 years' adjuvant oral tamoxifen (20 or 30 mg daily) were randomised to receive 1 mg oral anastrozole (n=1618) or 20 or 30 mg tamoxifen (n=1606) daily for the remainder of their adjuvant therapy. The primary endpoint was event-free survival, with an event defined as local or distant metastasis, or contralateral breast cancer. Analysis was by intention to treat.

Findings: 3224 patients were included in analyses. At a median follow-up of 28 months, we noted a 40% decrease in the risk for an event in the anastrozole group as compared with the tamoxifen group (67 events with anastrozole vs 110 with tamoxifen, hazard ratio 0.60, 95% CI 0.44-0.81, p=0.0009). Both study treatments were well tolerated. There were significantly more fractures (p=0.015) and significantly fewer thromboses (p=0.034) in patients treated with anastrozole than in those on tamoxifen.

Interpretation: These data lend support to a switch from tamoxifen to anastrozole in patients who have completed 2 years' adjuvant tamoxifen.

Publication types

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

MeSH terms

  • Aged
  • Anastrozole
  • Antineoplastic Agents, Hormonal / adverse effects
  • Antineoplastic Agents, Hormonal / therapeutic use*
  • Aromatase Inhibitors / adverse effects
  • Aromatase Inhibitors / therapeutic use*
  • Breast Neoplasms / drug therapy*
  • Breast Neoplasms / metabolism
  • Breast Neoplasms / mortality
  • Breast Neoplasms / pathology
  • Disease Progression
  • Disease-Free Survival
  • Female
  • Humans
  • Nitriles / adverse effects
  • Nitriles / therapeutic use*
  • Postmenopause
  • Prospective Studies
  • Randomized Controlled Trials as Topic
  • Receptors, Estrogen / analysis
  • Tamoxifen / adverse effects
  • Tamoxifen / therapeutic use*
  • Triazoles / adverse effects
  • Triazoles / therapeutic use*

Substances

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