The ATAC ('Arimidex', tamoxifen, alone or in combination) adjuvant breast cancer trial: First results of the endometrial sub-protocol following 2 years of treatment

S. Duffy*, T. L. Jackson, M. Lansdown, K. Philips, M. Wells, S. Pollard, G. Clack, M. Coibion, A. R. Bianco, J. Adams, M. Baum, A. Buzdar, D. Cella, R. Coleman, M. Constenla, J. Cuzick, W. Distler, M. Dowset, R. Eastell, L. J. FallowfieldJ. Forbes, W. D. George, J. Gray, J. P. Guastalla, R. Hellmund, G. Hoctin-Boes, J. Houghton, N. Williams, A. Howell, J. G.M. Klijn, G. Y. Locker, J. Mackey, R. E. Mansel, J. M. Nabholtz, T. Naglkalnai, A. Nicolucci, U. Nylen, R. Sainsbury, F. Sapunar, V. J. Suarez-Mendez, J. S. Tobias, M. Friedlander, G. Richardson, A. Makar, P. Neven, Guastalla, J. Mention, D. W. Distler, W. Eiermann, M. Mouritis

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

50 Scopus citations


Background: Tamoxifen treatment results in a doubling of the risk of endometrial cancer after 1-2 years of treatment and a quadrupling after 5 years. Anastrozole, a third-generation aromatase inhibitor, with superior efficacy to tamoxifen, may also offer tolerability benefits in terms of effects on the endometrium. Methods and results: A sub-protocol of the ATAC trial compared the incidence/type of intrauterine changes following treatment with these agents in a subgroup of patients (n = 285) from the main trial. After 2 years anastrozole treatment, endometrial thickness remained ≤ 5 mm (baseline: 3.0 mm); in patients receiving tamoxifen, endometrial thickness increased by 3.2 mm to 7.0 mm, with a similar trend in the combination group. At baseline, 26/285 patients (9.1%) had endometrial abnormalities, most commonly polyps. After 2 years the number of endometrial abnormalities appeared lower with anastrozole treatment compared with tamoxifen although these differences were not statistically significant (odds ratio: 0.44; 95% confidence interval 0.146, 1.314; P = 0.14). Most abnormalities occurred within the first year of treatment (anastrozole: 4/6; tamoxifen: 7/10; combination: 10/16; total: 21/32). Fewer patients in the anastrozole group (1.4%) required medical intervention (tamoxifen 12.5%; combination 13.6%). Conclusions: Fewer endometrial abnormalities occurred during 2 years treatment with anastrozole compared with tamoxifen although statistical significance was not reached in this sub-protocol analysis.

Original languageEnglish (US)
Pages (from-to)545-553
Number of pages9
JournalHuman Reproduction
Issue number2
StatePublished - Feb 1 2006


  • ATAC
  • Anastrozole
  • Breast cancer
  • Endometrial pathology
  • Tamoxifen

ASJC Scopus subject areas

  • Reproductive Medicine
  • Obstetrics and Gynecology


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