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World’s Largest Breast Cancer Treatment Trial Supports Anastrozole Use

World’s Largest Breast Cancer Treatment Trial Supports Anastrozole Use

New data presented at the recent San Antonio Breast
Cancer Symposium demonstrated that anastrozole (Arimidex), as an adjuvant
treatment in postmenopausal women with early breast cancer, significantly
reduced disease recurrence. After a median follow-up of 33.3 months and a median
duration of treatment of 30.7 months, 317 of 3,125 women in the anastrozole
group relapsed or died, compared with 379 of 3,116 women in the tamoxifen (Nolvadex)
group (P = .0129). This represents a 17% reduction in the risk of disease
recurrence with anastrozole treatment. Among women in the anastrozole group with
confirmed hormone-sensitive tumors, the reduction in risk of recurrence was 22%
compared to the tamoxifen group (P = .0054).

The new data are the first results from the ATAC (Arimidex, Tamoxifen Alone
or in Combination) study. The principal US investigator, Aman Buzdar, MD, of The
University of Texas M. D. Anderson Cancer Center in Houston, said the outcome
was important for postmenopausal women with early breast cancer. "Now after
20 years, tamoxifen’s established benefits in early breast cancer are being
challenged," he said. "Tamoxifen is a very effective drug, but it has
side effects, like an increased risk of endometrial cancer, that have to be
managed. The goal of research in this area is to improve that profile."

Trial Design

The multicenter, randomized, double-blind study involved 9,366 patients from
380 cancer centers in 21 countries. Enrollees consisted of early breast cancer
patients who had completed primary surgery and chemotherapy (if given) and were
candidates for adjuvant hormonal therapy. The trial was designed to determine if
anastrozole is equal to, or more effective than, tamoxifen, and whether
anastrozole offers additional safety and tolerability benefits. The study also
included a combination treatment arm (tamoxifen plus anastrozole) to determine
whether taking both medications together was better than taking tamoxifen alone.

Participants were randomized to receive anastrozole (1 mg daily), tamoxifen
(20 mg daily), or a combination of the two agents for 5 years or until disease
recurrence. Primary end points were disease-free survival and safety. Secondary
end points were time to distant recurrence and survival. No additional benefit
was seen with the combination arm over tamoxifen alone. In the combination
group, 383 of 3,125 women relapsed or died, compared to 379 of 3,116 of women in
the tamoxifen group.

Adverse Effects Contrasted

Anastrozole was associated with significantly fewer reports of endometrial
cancer, thromboembolic events, and vaginal bleeding than tamoxifen. In terms of
adverse events, deep-vein thrombosis was reported in 1.7% of the patients taking
tamoxifen compared to 1.0% of the anastrozole recipients. Endometrial cancer
occurred at a rate of 0.5% with tamoxifen compared to 0.1% with anastrozole.
Vaginal bleeding was reported in 8.1% of tamoxifen patients and 4.5 % of
anastrozole patients. Hot flashes (39.7% vs 34.3%) and weight gain (11.0% vs
9.2%) were also more common among women treated with tamoxifen, compared to
those taking anastrozole.

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