Personalized neoadjuvant strategy using 70-gene assay to increase breast-conserving surgery in ER+/HER2- breast...

We investigated whether tailored neoadjuvant therapy (chemotherapy [NCT] or endocrine therapy [NET]) guided by a 70-gene assay could improve breast-conserving surgery (BCS) rates among patients with ER-positive/HER2-negative breast cancer initially deemed ineligible for BCS. Of 130 prospectively enrolled patients (stage II-IIIA, across four Korean centers), 92 were analyzed. Patients classified as high genomic risk received NCT, while low-risk patients underwent NET (letrozole ± leuprolide for premenopausal women) for 16-24 weeks. The primary endpoint-achieving the surgeon-defined target tumor size for BCS-was reached in 69.6% (95% CI: 59.1-78.7%), significantly surpassing the predefined goal of 50.8% (p < 0.05). The actual overall BCS rate was 59.8% (64.7% NCT, 45.8% NET). Pathologic complete response occurred in 2.2%, exclusively in the NCT group. Thus, pretreatment genomic profiling effectively guided therapy selection, substantially increasing BCS eligibility while sparing low-risk patients unnecessary chemotherapy toxicity.