Multicenter prospective trial of omission of radiotherapy after breast-conserving surgery in women with low clinical and genomic risk breast cancer

Multiple studies have shown a low risk of ipsilateral breast events (IBEs) for selected patients aged 65 years or older with stage I breast cancers treated with breast-conserving surgery (BCS) and endocrine therapy (ET) without adjuvant radiotherapy. The multicenter prospective IDEA study in the USA evaluated whether younger postmenopausal patients could also be succesfully treated without radiation therapy, adding a genomic assay to classic selection factors. Patients had pT1N0 unifocal invasive breast cancer with margins ≥ 2 mm after BCS whose tumors were ER-positive and HER2-negative with Oncotype EX 21-gene recurrence score ≤ 18. Among 186 patients with follow-up of at least 56 months after BCS, overall and breast-cancer specific survival rates were both 100%. The 5-year freedom from any recurrence was 99% (n=2), while 6 additional patients had recurrence later than 5 years after BCS. The authors conclude that adding a genomic assay to classic clinical and biologic criteria for avoiding radiotherapy after BCS resulted in low risk of recurrence among younger postmenopausal patients with low-risk breast cancer.