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Extended adjuvant therapy fails to improve outcomes in hormone receptor-positive breast cancer
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SAN ANTONIO — Postmenopausal women with hormone receptor-positive breast cancer who underwent 5 additional years of extended anastrozole therapy received no additional benefit compared with women who underwent 2 additional years of therapy, according to data from the ABCSG-16 phase 3 trial presented at the San Antonio Breast Cancer Symposium.
The shorter duration of treatment provided sufficient benefit while additionally protecting women from common adverse events, including bone fractures, hot flashes, arthralgia and hair loss.
“These trial results should be implemented into daily practice at once,” Michael Gnant, MD, FACS, director and chairman of the department of surgery at the Comprehensive Cancer Center of Medical University of Vienna, said during a press briefing. “There is simply no rationale to keep most patients on extended aromatase inhibitors for longer than 2 years. This result can help save a lot of unnecessary side effects for many women around the world.”
Previous research has shown that extending adjuvant therapy with aromatase inhibitors after 5 initial years of tamoxifen therapy is beneficial for postmenopausal women with hormone receptor-positive breast cancer. However, the appropriate duration of extended adjuvant therapy has been less clear.
For this reason, Gnant and colleagues sought to assess and compare the effect of an additional 2 years vs. 5 years of anastrozole after 5 years of adjuvant endocrine therapy.
Between February 2004 and June 2010, researchers randomly assigned 3,484 postmenopausal women (median age, 64 years) with hormone receptor-positive early-stage breast cancer receiving treatment across 71 centers in Austria to one of these two extended treatment schedules. Prior to randomization, 51% of patients had received 5 years of tamoxifen, whereas 49% had received other aromatase inhibitor-containing regimens.
DFS served as the study’s primary outcome; secondary outcomes included OS, contralateral breast cancer, fracture and toxicity.
At a median follow-up of 9 years, 78% of women in both arms were alive without disease recurrence; 22% of women in each arm experienced disease recurrence.
The researchers observed no significant differences in DFS (HR = 1.007; 95% CI, 0.87-1.16), OS (HR = 1.007; 95% CI, 0.82-1.23) or time to contralateral breast cancer between the two arms.
However, more women in the 5-year arm experienced bone fractures than women in the 2-year arm (6.3% vs. 4.7%; HR = 1.35; 95% CI, 1-1.84).
“Bone fractures were more common during years 3 and 5 after randomization. Thus, the longer duration of anastrozole may be a risk factor for fractures,” Gnant said. “Future translational research using data and biomaterial from the patients in the ABCSG-16 trial could be useful to characterize potential molecular factors that influence patients’ response to anastrozole.” – by Jennifer Southall
Reference:
Gnant M, et al. Abstract GS3-01. Presented at: San Antonio Breast Cancer Symposium; Dec. 5-9, 2017; San Antonio.
Disclosures: AstraZeneca funded this study. Gnant reports funding from AstraZeneca. Please see the abstract for all other authors’ relevant financial disclosures.
Perspective
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Endocrine therapy is an extremely important treatment modality for ER-positive breast cancers. At this point, we know that 5 years of endocrine therapy is extremely important to reduce cancer recurrence. For patients treated with tamoxifen for 5 years, we can extend the treatment for 5 additional years with either tamoxifen or an aromatase inhibitor. The data are clear on these two fronts.
The big question is the role of 5 years of extended aromatase inhibitors after 5 years of aromatase treatment. This particular Austrian study looked at the optimal duration of the extended adjuvant treatment. The study included more than 3,000 patients with a median follow-up of more than 100 months. Results showed no difference in DFS and OS for 5 years compared with 2 years of extended adjuvant therapy; however, there was an increased number of fractures among those assigned the 5-year arm. So, based upon this study, we can say that the additional 5 years of an aromatase inhibitor did not add to the 2 years of extended therapy. We are still not clear who will benefit from extended treatment vs. 5 years. Potentially robust biomarkers will guide us to select the right patients for extended adjuvant therapy.
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