Use of the 21-gene recurrence score (RS) combined with response to 3-week preoperative endocrine therapy can be used to guide systemic therapy in early breast cancer patients with limited nodal involvement, and can help avoid overtreatment with chemotherapy, according to German investigators.
Among patients with early, hormone receptor (HR)-positive/HER2-negative breast cancer, the 5-year invasive disease-free survival (iDFS) rate with endocrine therapy alone was a similar 92.6% for those who showed a response to endocrine therapy but had an intermediate RS (12-25; experimental group) and 93.9% for patients with a low RS (0-11; control group).
The one-sided 95% lower confidence limit of the 5-year iDFS difference was -3.3%, establishing prespecified noninferiority (P=0.05), reported Nadia Harbeck, MD, PhD, of LMU University Hospital in Munich, and colleagues in the Journal of Clinical Oncology.
"On the basis of multicenter prospective phase III data from 2,290 patients with a 60-month median follow-up, the WSG-ADAPT-HR+/HER2- endocrine trial shows that -- independent of their age -- a substantial proportion of these patients can safely be treated by adjuvant ET [endocrine therapy] alone: not only patients with 0-3 involved lymph nodes and RS 0-11, but also those with limited nodal burden, RS 12-25, and Ki67 response after short preoperative ET," the authors wrote.
This combination approach can help to avoid chemotherapy in more than half of patients who otherwise would be candidates for treatment by conventional clinicopathologic criteria, they added.
As for key secondary endpoints, the 5-year distant DFS rate was 95.6% in the experimental arm versus 96.3% in the control arm, while the 5-year overall survival rates were 97.3% versus 98.0%, respectively.
Survival differences were similar between age subgroups and according to nodal status.
This study showed that short-term presurgical therapy can provide additional useful information around the RS test cutoff of 25, noted Mitch Dowsett, PhD, of Royal Marsden Hospital in London, in an editorial accompanying the study.
"What is incontrovertible is that short-term presurgical therapy provides an excellent scenario for discovery of biomarkers of resistance to ET," he observed. "These studies have the potential to identify resistance mechanisms in those patients with high [post-endocrine] Ki67 and to guide the selection of agents targeted to the respective mechanism alongside their adjuvant endocrine treatment."
The study's intention-to-treat population included 2,290 patients; 1,422 in the experimental arm (26.3% premenopausal, median age 58) and 868 in the control arm (34.6% premenopausal, median age 57).
Patients received induction preoperative endocrine therapy for 3 weeks, usually tamoxifen in premenopausal patients and aromatase inhibitors in postmenopausal patients. During this induction therapy, RS was assessed using Oncotype DX, with patients classified as low RS (RS 0-11), intermediate RS (RS 12-25), or high RS (RS >25). Central Ki67 measurements were obtained at baseline and after preoperative endocrine therapy.
In a group of 694 patients with intermediate RS, but who did not respond to endocrine therapy and went on to receive dose-dense chemotherapy, 5-year rates were 90.3% for iDFS, 92.8% for DFS, and 96.7% for overall survival.
Endocrine therapy response was more likely with aromatase inhibitors than with tamoxifen -- 78.1% versus 41.1% (P<0.001). Endocrine therapy response was 78.8% in patients with an RS of 0-11, 62.2% in those with an RS of 12-25, and 32.7% in those with an RS >25.
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Disclosures
The trial was sponsored by the West German Study Group.
Harbeck reported stock and other ownership interests in the West German Study Group, and relationships with Amgen, AstraZeneca, Daiichi Sankyo, Exact Sciences, Lilly, MSD, Novartis, Pierre Fabre, Pfizer, Roche/Genentech, Sandoz, and Seattle Genetics.
Other co-authors reported multiple relationships with industry.
Dowsett reported honoraria from NanoString Technologies, Lilly, and BCNscience; consulting or advisory roles with Zentalis, AstraZeneca/MedImmune, Besins Healthcare, Roche, Agilent, and Rovi; and research funding from Pfizer and Lilly.
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