SAN ANTONIO—In the largest breast cancer trial ever conducted, anastrozole(Drug information on anastrozole) (Arimidex) emerged the winner in a head-to-head comparison with tamoxifen(Drug information on tamoxifen) (Nolvadex) in early-stage breast cancer. The impressive results, in both efficacy and tolerability, were reported at the 24th Annual San Antonio Breast Cancer Symposium (abstract 8).
The findings were the first results from the large ATAC trial (Arimidex and Tamoxifen Alone or in Combination), being conducted in 380 cancer centers in 21 countries. The study involves 9,366 postmenopausal women with operable breast cancer, randomized after surgery and primary chemotherapy to anastrozole 1 mg daily, tamoxifen 20 mg daily, or the combination.
Professor Michael Baum, of University College Hospital, London, presented the first data on recurrence-free survival and incidence of contralateral breast cancer, based on a median 33 months follow-up and median treatment duration of 31 months.
The analysis showed that 317 of 3,125 women in the anastrozole group had a relapse of their breast cancer or died, compared with 379 of 3,116 women in the tamoxifen group (P = .0129), representing a 17% reduction in the risk of recurrence in favor of anastrozole. In women with hormone-sensitive tumors, the reduction in risk of recurrence was 22% with anastrozole (P = .0054).
Anastrozole also reduced the risk of contralateral breast cancer by 58% over tamoxifen (P = .0068), "providing an additional reduction of almost 60% over the 50% already produced by tamoxifen," Dr. Baum said.
There was no additional efficacy benefit with the combination over tamoxifen alone. In the combination group, 383 of 3,125 women had a relapse or died. Dr. Baum said the trials’ endocrinologists speculate that "in a very low estrogen environment provided by anastrozole, tamoxifen is seen as an estrogen agonist, rather than antagonist," thus counteracting a treatment effect.
Aman Buzdar, MD, principal US investigator for the study, described the outcome as extremely important. "Now, after 20 years, tamoxifen’s established benefits in early breast cancer are being challenged," said Dr. Buzdar, of M.D. Anderson Cancer Center.
