Hormonal Receptor (HR)-Positive HER2 Negative Breast Cancer Patients Treated With Preoperative ELacestrant and PULSAR Radiotherapy

This is a proof-of-concept phase II trial to assess the safety (as primary endpoint) and clinical efficacy of neoadjuvant therapy with Elacestrant and PULSAR. The study will enroll 21 postmenopausal patients with early HR+ HER2- node positive BC, clinically staged II-III. Patients will receive Elacestrant 345 mg orally once daily for 24 weeks and PULSAR on the MRI-based breast gross tumor volume (GTVt), consisting of 10 Gy "pulse" every 4 weeks for a maximum of 5 or less in case of radiologic complete response. Surgery will be planned 24 weeks after Elacestrant initiation and at least 2 weeks from the last pulse and will be performed as per recommended clinical practice. Patients will then receive adjuvant systemic therapy as per standard of care and postoperative RT to the locoregional lymph nodes in case of nodal residual disease, if indicated.