Single-Fraction Pre-Operative Stereotactic Radiosurgery for Early-Stage Breast Cancer: Pathological Findings

Abstract

to assess pathological results after single-fraction pre-operative stereotactic radiosurgery of early-stage breast cancer. A phase 2 clinical trial to investigate the feasibility of pre-operative radiosurgery for early-stage breast cancer was conducted. Eligible patients are women older than 50 years, with histologically proven breast invasive ductal carcinoma, hormonal receptors positive/human epidermal grow factor receptor 2 negative, any grade, tumor size < 3cm, unifocal, with no nodal involvement, and suitable for breast conservative surgery. An expert radiologist injected ultrasound-guided a fiducial marker to precisely identify tumor positioning. The Planning Target Volume (PTV) is created by adding a 3mm margin to the Gross Tumor Volume (GTV). A single fraction of 30-33 Gy is delivered to 95% of PTV. Patients had a breast MRI scan 6-12 weeks after treatment to evaluate the rate of radiological response. Surgery was performed at 9 to 16 weeks after irradiation. From January 2022 to December 2022, 33 patients underwent single-fraction radiosurgery, of whom 29 had breast conserving surgery (BCS). BCS was performed at 9-10 weeks for the first 14 patients, at 14-16 weeks for 13 patients, and at 18-19 weeks for 2 patients. The pathological response was defined as complete response (pCR) if no residual tumor cells were found, partial response (pPR), or no response. The pPR were also subdivided into 3 subgroups according to the rate of residual disease: < 10%, 10-50%, and > 50%. Two patients (7%) achieved pCR, both treated with 33 Gy and operated at 14 weeks. Twenty-five patients (86%) had pPR, of which 7 patients (24%) had residual disease < 10%, 9 patients (31%) between 10-50% and 9 patients (31%) over 50%. Two patients (7%) had no pathological response. All patients had sentinel lymph node biopsy at the time of surgery. Positive micrometastatic nodal involvement was found in 3 patients (11%), of which 2 patients (7%) had macrometastases (pN1a) and received subsequent axillary lymph node dissection. All patients had negative surgical margins. Not any acute and sub-acute surgical complications were observed. Single-fraction pre-operative stereotactic radiosurgery for early-stage breast cancer leads to a high rate of complete or partial pathological response with surgery performed at 2-4 months following irradiation.