SAN ANTONIO, Dec. 14 — Even after the end of treatment, anastrozole (Arimidex), an aromatase inhibitor, outperforms tamoxifen in women with hormone-receptor-positive early breast cancer, a researcher said here.
The finding came after a median of 100 months of follow-up of the 5,216 postmenopausal women with localized invasive breast cancer in the landmark Arimidex, Tamoxifen, Alone, or In Combination (ATAC) trial, according to John Forbes, M.D., of the University of Newcastle in Australia.
At the median 100-month follow-up, time to recurrence, time to distant recurrence, and contralateral breast cancer were improved significantly in the intent-to-treat and hormone-receptor-positive populations, the investigators found.
More than three years, on average, after women in the study stopped taking the medications, those in the anastrozole arm had a 15% lower risk of recurrence than those in the tamoxifen arm, Dr. Forbes told an oral session at the San Antonio Breast Cancer Symposium. The full results of the study were reported simultaneously online in Lancet Oncology.
The absolute difference between the two arms in the proportion of women who relapsed nearly doubled in the four years after the end of treatment, Dr. Forbes said — from 2.8% to 4.8%.
“This is the first demonstration of a carry-over effect for aromatase inhibitors,” he said.
One new element after 100 months was the discovery that the increased rate of fractures associated with anastrozole — a well-known side effect of the aromatase inhibitor — vanished once the treatment drug was stopped after five years, he said.
The study’s North American leader, Aman Buzdar, M.D., of M. D. Anderson Cancer Center in Houston, said that finding “is totally new.”
“The downside of anastrozole was the increased risk of fractures,” he said in an interview. But “once you stop taking the drug, the risk of fractures drops very quickly.”
During the five years of active treatment, the researchers said, the annual fracture rate for women getting anastrozole was 2.93% versus 1.9% for those on tamoxifen and the incidence rate ratio was 1.55, which was significant at P