SAN ANTONIO – Women who took the aromatase inhibitor anastrozole (Arimidex) for an extra 2 years beyond the current standard 5 years of treatment, for purposes of preventing breast cancer recurrence, received the same benefit in disease control as women who took the drug for an extra 5 years, researchers reported here.
Among women who stopped extension treatment with anastrozole after 2 years, 71.1% were alive and free of disease, compared with 70.3% of women who stayed on it for 5 years (P=0.925), said Michael Gnant, MD, of the University of Vienna, in reporting results of the prospective, randomized Austrian Breast and Colorectal Cancer Study Group-16 trial.
In his oral presentation at the annual San Antonio Breast Cancer Symposium, the only difference Gnant observed was that women who continued on anastrozole for 5 years experienced a slight increase in fracture rates that fell just short of statistical significance – 6.3% of women taking the drug for 5 years versus 4.7% of the women who discontinued after 2 years (P=0.053).
There was no statistically significant difference in overall survival. The overall survival from time to randomization to death of any cause was 85.4% of women who were assigned to the 2-year extension with anastrozole and 84.9% of women who were assigned to 5 years of treatment with anastrozole (P=0.947), Gnant said.
“After 5 years of standard endocrine therapy, 2 additional years of anastrozole are sufficient,” he suggested. “There is no benefit of continuing/escalating endocrine treatment beyond 7 years.”
Gnant said the study was initiated because even 5 years after endocrine therapy breast cancer still recurs. “More than 50% of breast cancer recurrences occur after the first 5 years of follow-up after initial treatment of breast cancer,” he said. “Since the risk of recurrence persists, extending adjuvant therapy is appealing.”
Currently, more women diagnosed with hormone positive breast cancer are treated with tamoxifen or aromatase inhibitors for 5 years, but Gnant said the optimal duration of extension beyond that is controversial, and was the aim of ABCSG-16 to define.
The researchers enrolled 3,469 women who were recruited from 75 centers in Austria. All the women had completed 4-6 years of therapy with either tamoxifen or an aromatase inhibitor or both. The researchers assigned 1,731 women to 2 years of treatment with anastrozole and 1,738 women to 5 years of treatment with anastrozole.
Gnant said a deep dive into the data found no subgroup of patients who did better than others, including specific age groups, tumor stages, nodal status, receptor positivity, or previous chemotherapy. Any way the data were sliced, the results were the same – no significant differences between those treated for 2 years or for 5 years.
Gnant and colleagues also examined adherence factors in the trial, but again there was no outcome difference depending on the level of adherence.
What is needed next, he said, “is translational research that may identify molecular characteristics that indicate benefit of prolonged extended therapy.”
In commenting on the study, session moderator Carlos Arteaga, MD, director of the Harold C. Simmons Comprehensive Cancer Center at the University of Texas Southwestern at Dallas, told MedPage Today, “This was a negative study, with positive news. We should be looking at ways of shortening therapy. We can’t just keep extending and extending and extending. We need to come up with better ideas.”
“For a long time we have treated too many women for too long a time,” Arteaga said. “We should give deescalation of therapy a try at least in hormone-positive breast cancer. In triple-negative breast cancer we are still escalating treatment but it has a very positive result.”
However, he cautioned that de-escalation should be performed in the context of controlled clinical trials. “In the process of de-escalating, we may be depriving someone of treatment, so we have to be very careful about that – such as the studies presented today,” he said.
Arteaga relevant relationships with Roche, Monogram (LabCorp), AstraZeneca, Novartis, Genentech and Susan G. Komen.
Gnant disclosed relevant relationships with Sandoz, Roche, Novartis. AstraZeneca, Celgene, GSK, Amgen, OBI-Pharma, Ipsen, Nanostring, Accelsiors, Pfizer and Eisai.
F. Perry Wilson, MD, MSCE Assistant Professor, Section of Nephrology, Yale School of Medicine and Dorothy Caputo, MA, BSN, RN, Nurse Planner