HOUSTONThe nonsteroidal aromatase inhibitor anastrozole (Arimidex)
continues to outperform tamoxifen in every efficacy measurement in the Arimidex,
Tamoxifen, Alone or in Combination (ATAC) trial, according to a recent 47-month
update. Speaking for the ATAC Trialists’ Group, Aman U. Buzdar, MD, professor
of medicine and deputy chairman of the Department of Breast Medical Oncology at
The University of Texas M.D. Anderson Cancer Center, Houston, reported that the
absolute differences between the two drugs are increasing with time.
The 5-year ATAC trial, which is being conducted at 381 centers in 21
countries, is evaluating anastrozole, tamoxifen, or a combination of the two
among 9,366 postmenopausal women with invasive breast cancer. The median age of
the group is 64, and 34% of the patients were node-positive at diagnosis. All
had completed primary therapy (surgery with or without radiotherapy and/or
chemotherapy) before entering the trial. The breakdown of hormone-receptor
status in the ongoing trial is 84% positive, 8% negative, and 8% unknown.
Past and Current Updates
The previous ATAC follow-up, at a median of 33.3 months, analyzed 1,079
first events (Lancet 359:2131-2139, 2002). In that analysis, the
anastrozole-alone group had a disease-free survival of 89.4% compared to 87.4%
for the tamoxifen-alone group. Disease-free survival in the combination group
was 87.2%, similar to that of the tamoxifen-alone group.
At a median follow-up of 47 months, 1,373 first events had occurred.
Virtually no differences were found in the tamoxifen alone group and the
tamoxifen plus anastrozole groups. Looking just at the monotherapy arms, 413
first events had occurred in the anastrozole (1 mg per day) group and 472 in
the tamoxifen (20 mg per day) group. Events in the anastrozole group included
84 locoregional recurrences, 195 distant recurrences, 20 contralateral
(invasive) cancers, and 5 contralateral ductal carcinoma in situ (DCIS). Among
the tamoxifen group, there were 101 locoregional recurrences, 222 distant
recurrences, 35 contralateral (invasive) cancers, and 5 contralateral DCIS. In
each treatment group, 109 women died before experiencing a recurrence.
Advantage May Be Increasing
In the overall population, disease-free survival for patients in the
anastrozole arm was 86.9% compared to 84.5% for those in the tamoxifen arm. The
hazard ratio for disease-free survival was 0.86. When nonbreast cancer deaths
were excluded, the hazard ratio improved to 0.83, or a 17% reduction in the
probability of breast cancer recurrence among the anastrozole-treated patients.