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Anastrozole Protective Against Endometrial Cancer: Presented at EBCC

By Paula Moyer

HAMBURG, GERMANY -- March 22, 2004 -- Women who receive anastrozole (Arimidex) therapy for the treatment of breast cancer may have a lower risk of endometrial cancer than women in the general population, according to findings presented here March 18^th at the 4^th European Breast Cancer Conference.

This finding is good news, because the standard first-line adjuvant therapy, tamoxifen, is known to carry an increased risk of endometrial cancer, said presenting investigator Sean Duffy, MD, Oncologist, St. James University Hospital, Leeds, United Kingdom.

Investigators noted, in a recent analysis of data from the Arimidex, Tamoxifen, and Combination (ATAC) trial, that anastrozole had 0.1% risk of endometrial cancer in comparison to tamoxifen's 0.5% risk. The investigators therefore decided to compare the endometrial-cancer incidence rates seen with anastrozole in the ATAC trial to women in an age-matched standard population, to see if anastrozole actually offered protective benefit.

The investigators obtained age-specific endometrial-cancer rates, expressed per 1,000 patient years, for the United States and for Europe. The United States data were obtained from the United States Surveillance, Epidemiology and End Results Surveillance, Epidemiology and End Results (SEER) data, and the European data were obtained from the European cancer registry (EUCAN). Both were adjusted for the prevalence of hysterectomy.

Dr. Duffy and his co-investigators then calculated the expected incidence of endometrial cancer in each age-specific group from the ATAC trial, which was categorised by North American and European patients. The patients' duration of follow-up was then calculated and compared with the observed incidence, from which a Standard Incidence Rate (SIR) was calculated with a 95% confidence interval.

In the anastrozole group, the investigators documented an observed incidence of 3 cases per approximately 5,300 patient years, compared with an expected incidence of 4.14. The SIR for anastrozole patients was 0.73. For patients treated with tamoxifen, the observed incidence was 11 per 5,300 patient years, with an expected incidence of 4.10 and an SIR of 2.68. For those on combination therapy, the observed incidence was 5 per 5,300 patient years, with an expected incidence of 4.10 and an SIR of 1.22.

The findings showed that patients on anastrozole had a lower rate of endometrial cancer than would be expected in a normal age-matched population, Dr. Duffy said. "The data show that anastrozole has a probable protective effect against endometrial cancer development, and that randomised trials to assess the effectiveness of anastrozole as a treatment for endometrial cancer may be warranted," said Dr. Duffy.


[Study Title: Anastrozole Has a Protective Effect on the Endometrium: Data From the ATAC (`Arimidex', Tamoxifen, Alone or in Combination) Trial. Abstract 290]

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