The 10-year follow-up of the ATAC trial (Arimidex, Tamoxifen,
Alone or in Combination) upholds the disease control advantage seen
for anastrozole over tamoxifen in the longest running clinical
trial of aromatase inhibitors in early breast cancer. The new data
were presented at the 2010 Breast Cancer Symposium.1
"At 10 years of median follow-up, anastrozole is significantly
superior to tamoxifen in preventing breast cancer recurrences,"
reported Aman Buzdar, MD, of The University of
Texas M. D. Anderson Cancer Center, Houston.
At 10 years, patients on the anastrozole arm
experienced an absolute 4.3% reduction in recurrence risk compared
with patients treated with tamoxifen, amounting to a 21% relative
risk reduction. This is an increase over the 2.7% absolute
difference observed at completion of therapy, which occurred at 60
months. Blinding of the study has been maintained over time.
Although patients on the aromatase inhibitor experienced more
fractures and arthralgia while on treatment, at 10 years (5 years
off treatment) these differences had disappeared. During the study,
the anastrozole group had a 33% increase in risk of fracture
(P < .0001) but this equalized by year 6, when patients
went off the drug.
ATAC randomly assigned 6,241 postmenopausal women to 5 years of
anastrozole or tamoxifen. At 10 years, recurrences were observed in
24.0% of the tamoxifen arm compared with 19.7% of the anastrozole
arm (P = .0002). At 60 months, recurrences were seen in
12.5% and 9.8%, respectively.
Carryover Effect
"Recurrence rates continue to be lower with anastrozole after
treatment completion," Dr. Buzdar said. "The absolute difference in
recurrence increased, and there was a statistically significant
larger carryover effect for anastrozole after 5 years." This
carryover effect amounted to a risk reduction in years 5 through 9
of 50% with anastrozole, compared with 33% for tamoxifen
(P = .03), which has been reported with tamoxifen overview
data from Oxford Trialists Group, he added.
Distant recurrence risk at 10 years was 17.7% with
anastrozole and 15.1% with tamoxifen, for a 15% relative risk
reduction (P = .02). Contralateral breast cancers occurred
in 4.9% and 3.2%, respectively, for a 36% reduction (P =
.003). Deaths occurred in approximately 24% in each arm.
Jennifer C. Obel, MD, of NorthShore University
HealthSystems in Evanston, Illinois, served as a spokesperson to
the press at the meeting. She commented, "Women want to know not
only what the side effects of these drugs are on them today, but
what the side effects are over time. These findings also reassure
patients that the superiority of an aromatase inhibitor, compared
to tamoxifen, holds up at 10 years, and continues to reduce their
risk of recurrence." ■
Reference
1. Buzdar A, Cuzick J, Sestak I, et al: Ten-year analysis of the
ATAC trial. 2010 Breast Cancer Symposium. Abstract 256. Presented October 2, 2010.
