The results provide the “strongest evidence to date on the short-term safety of this choice,” Sharon Giordano, MD, MPH, with University of Texas M.D. Anderson Cancer Center, Houston, wrote in an editorial accompanying the study.
“Physicians should now incorporate these positive data into their shared decision-making process with patients,” Dr. Giordano said.
The POSITIVE trial findings were published online in The New England Journal of Medicine.
Before the analysis, the risks associated with taking a break from endocrine therapy among young women with hormone receptor (HR)–positive breast cancer remained unclear.
In the current trial, Ann Partridge, MD, MPH, and colleagues sought prospective data on the safety associated with taking a temporary break from therapy to attempt pregnancy.
The single-group trial enrolled more than 500 premenopausal women who had received 18-30 months of endocrine therapy for mostly stage I or II HR-positive breast cancer. After a 3-month washout, the women were given 2 years to conceive, deliver, and breastfeed, if desired, before resuming treatment. Breast cancer events – the primary outcome – were defined as local, regional, or distant recurrence of invasive breast cancer or new contralateral invasive breast cancer.
The results, initially reported at San Antonio Breast Cancer Symposium (SABCS) 2022, showed that a temporary interruption of therapy to attempt pregnancy did not appear to lead to worse breast cancer outcomes.
Among 497 women who were followed for pregnancy status, 368 (74%) had at least one pregnancy, and 317 (64%) had at least one live birth.
After a median follow-up of 3.4 years, 44 women had had a breast cancer event – a result that was close to, but did not exceed, the safety threshold of 46 breast cancer events.
The 3-year incidence of breast cancer events was 8.9% (95% confidence interval [CI], 6.3-11.6) in the treatment-interruption group compared with 9.2% (95% CI, 7.6-10.8) among historical controls, which included women who would have met the entry criteria for the trial.
“These results suggest that although endocrine therapy for a period of 5-10 years substantially improves disease outcomes in patients with hormone receptor–positive early breast cancer, a temporary interruption of therapy to attempt pregnancy does not appear to have an appreciable negative short-term effect,” wrote Dr. Partridge, vice chair of medical oncology at Dana-Farber Cancer Institute and professor of medicine at Harvard Medical School, Boston, and colleagues.
The authors cautioned, however, that the median follow-up was only 3.4 years and that 10-year follow-up data will be “critical” to confirm the safety of interruption of adjuvant endocrine therapy.
Dr. Giordano agreed, noting that “recurrences of breast cancer are reported to occur at a steady rate for up to 20 years after diagnosis among patients with hormone receptor–positive disease; the protocol-specified 10-year follow-up data will be essential to establish longer-term safety.”
The study was supported by the International Breast Cancer Study Group and by the Alliance for Clinical Trials in Oncology in North America in collaboration with the Breast International Group (BIG). Disclosures for authors and editorial writer are available at NEJM.org.
A version of this article first appeared on Medscape.com.