Women who stop adjuvant endocrine therapy after 5 years are still at substantial risk of distant recurrence over the next 15 years, even if their tumors were small, according to results of a recent meta-analysis of 88 clinical trials.
For women with T1N0 disease, the annual rate of distant recurrence was approximately 1% each year during 5-20 years, resulting in a cumulative risk of distant recurrence of 13%, authors of the meta-analysis reported (N Engl J Med. 2017 Nov. 8. doi: 10.1056/NEJMoa1701830).
Tumor diameter and nodal status was associated with the risk of distant recurrence during the later years and was approximately additive, with the risk increasing from 13% for T1N0 to 41% for T2N4–9 disease, wrote investigator Hongchao Pan, PhD, of the Nuffield Department of Population Health, University of Oxford, England, and his coauthors.
“Recognition of the magnitude of the long-term risks of ER-positive disease can help women and their health care professionals decide whether to extend therapy beyond 5 years and whether to persist if adverse events occur,” the authors wrote in the report.
The meta-analysis by Dr. Pan and his colleagues included 62,923 women with ER-positive breast cancer who were free of disease after 5 years of scheduled endocrine therapy.
They had hoped to identify a subgroup of women with a recurrence risks so small that the risk of additional side effects caused by extending endocrine therapy would outweigh any potential benefits of that additional treatment. However, the finding of measurable risk even in the women with T1N0 disease led them to recommend that extending endocrine therapy at least be considered for all patients.
“An absolute reduction of a few percentage points in the risk of distant metastases over the next 15 years might well be possible even for such low-risk women, with correspondingly greater absolute benefits for women with larger tumors or node-positive disease,” they wrote.
Whether reducing risk translates into improved survival remains to be seen.
As of now, “reliable trial evidence is not yet available” to confirm the clinical benefit of extending endocrine therapy beyond 5 years, the authors noted.
Cancer Research UK and others funded the study. Senior author Daniel F. Hayes, MD, reported grant support from Eli Lilly, Janssen Research & Development, Veridex, Puma, Pfizer, and AstraZeneca, among other disclosures. Full disclosures for all authors were provided on the NEJM website.