Younger postmenopausal patients with low-risk, stage I HR-positive breast cancer and certain genetic markers may be able to safely forgo adjuvant radiotherapy, according to study findings presented at the 2023 San Antonio Breast Cancer Symposium in Texas. 

In the IDEA (Individualized Decisions for Endocrine therapy Alone) trial, 200 postmenopausal patients with stage I HR-positive, HER2-negative breast cancer—all of whom had scores of 18 or less on the Oncotype DX recurrence assay—elected to skip adjuvant radiotherapy, provided they were willing to continue with endocrine therapy for 5 years. 

All participants were aged between 50 and 69 years and required to have a margin of 2 mm or more after breast-conserving surgery. The primary outcome was the rate of disease recurrence at 5 years after surgery. 

Patients had a mean recurrence score of 11.2. Eighty-five patients had grade 1 tumors, whereas 109 had grade 2 tumors and 6 had grade 3 tumors. The tumors were a mean of 10 mm. The median follow-up was 5.21 years. 

Both the overall survival rate and breast-cancer survival rate were 100% at 5 years, the researchers reported, with a 5-year freedom-from-recurrence rate of 99% (95% CI, 96-100). However, 2 patients died after the 5-year follow-up period had expired. 

There were two breast cancer related events during the follow-up period. One event, which occurred at the 21-month mark, was an isolated axillary recurrence. This was treated with axillary dissection and breast irradiation as well as local irradiation. The other was an ipsilateral breast event, which occurred at 49 months and was treated with another breast-conserving surgery. 

Another 6 patients experienced recurrence after the 5-year follow-up period, the researchers reported. Five of these were ipsilateral breast events, and one was an ipsilateral breast event with regional occurrence. For the entire follow-up period, the crude rate of ipsilateral breast events was 3.3% (n = 2 of 60) for patients who were 50 to 59 years old, and 3.6% (n = 5 of 140) for those who were 60 to 69 years old. The crude overall relapse rates in these age groups were 5% (n = 3) and 3.6%, respectively. 

“These findings indicate that younger postmenopausal patients with stage I breast cancer who skip radiotherapy after breast-conserving surgery have a very low risk of disease recurrence within 5 years. However, 5 years is an early time point for this population, and longer-term follow-up of this study and others will be essential to determine whether this option can be safely offered to women in this age group.”

- Reshma Jagsi, MD, DPhil, radiation oncologist at the Emory University School of Medicine and researcher at the Winship Cancer Institute of Emory University. 

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Reference:
Jagsi, R. Five-year outcomes of the IDEA trial of endocrine therapy without radiotherapy after breast-conserving surgery for postmenopausal patients age 50-69 with genomically-selected favorable stage I breast cancer. Abstract GS02-08. SABCS 2023.

Disclosures: Jagsi declared financial ties to drug makers. The study was funded by the Susan G. Komen Breast Cancer Foundation and the University of Michigan Rogel Cancer Center.

By Andrew John, MD /alert Contributor

Photo Credit: Getty Images.