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Anastrozole and exemestane yielded nearly identical clinical outcomes
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33rd Annual San Antonio Breast Cancer Symposium
SAN ANTONIO — Similar survival and recurrence prevention rates were observed among women treated with anastrozole or exemestane as adjuvant therapy, according to findings presented here at the 33rd Annual San Antonio Breast Cancer Symposium.
Paul E. Goss, MD, PhD, professor of medicine at Harvard Medical School, said anastrozole is a nonsteroidal inhibitor and exemestane is a steroidal inhibitor.
“Exemestane belongs to its own class,” Goss said. “The androgenic structure and androgenic effect may exert an antitumor effect through these androgenic properties and may cause fewer menopausal symptoms as a result.”
Goss used graphs to indicate that survival outcomes were similar between the two treatments.
“For event-free survival, the graphs were superimposable upon each other,” he said, noting that there was a nonsignificant probability value at a median follow up of 4.1 years.
“Subset analyses of node negative or positive status were again superimposable with HRs and P-values nonsignificant,” Goss said. “The same held true for overall survival and distant disease-free survival.”
About 70% of adverse events were grade 1 and 2, and the rest were grade 3 and 4.
“Vaginal bleeding was slightly more common with exemestane,” he said, adding that cardiovascular effects were nonsignificant, and clinical fractures were the same in the two arms.
“End-organ effects were slightly different between the two, which could be important,” Goss said.
Anastrozole is approved as adjuvant monotherapy in hormone receptor-positive early-stage breast cancer. The steroidal irreversible exemestane is approved in sequence after an initial 2 to 3 years of tamoxifen.
The current study tested the hypothesis that exemestane would have greater efficacy and better end-organ safety than anastrozole because it is irreversible and more potent than anastrozole; because it does not induce intra-tumoral aromatase; and because it may exert a second antitumor effect and more favorable profiles regarding bone and lipid metabolism.
Although the initial study also included a second tier that tested the role of celecoxib in combination therapy with an aromatase inhibitor, this treatment was discontinued because of cardiovascular toxicity.
There were 7,576 eligible women randomly assigned to adjuvant anastrozole at 1 mg per day or exemestane 25 mg per day with or without celecoxib 400 mg or placebo twice daily for 3 years. The trial began in June 2003 and ran through July 2008. Celecoxib was discontinued in December 2004, after 1,635 patients had received the drug.
The primary outcome measure was event-free survival. OS, distant recurrence, incidence of contralateral breast cancer and safety were secondary outcomes.
Baseline patient characteristics were similar between the two groups.
“Exemestane is comparable with anastrozole and may be a new option for 5-year adjuvant therapy,” Goss said, adding that compliance was equally poor for both agents and similar to other long-term agents.
“This was a superiority trial, but questions remain unanswered,” he said.
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