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Adjuvant Anastrozole Superior to Tamoxifen in Huge ATAC Breast Cancer Trial

Adjuvant Anastrozole Superior to Tamoxifen in Huge ATAC Breast Cancer Trial

SAN ANTONIO—In the largest breast cancer trial ever conducted,
anastrozole (Arimidex) emerged the winner in a head-to-head comparison with
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.

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