The ATAC ('Arimidex', Tamoxifen, Alone or in Combination) adjuvant breast cancer trial: first results of the endometrial sub-protocol following 2 years of treatment.

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
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.