Stereotactic image-guided neoadjuvant ablative single-dose radiation, then lumpectomy, for early breast cancer: the SIGNAL prospective single-arm trial of single-dose radiation therapy.

Background and Purpose: Adjuvant whole-breast irradiation after breast-conserving surgery, typically delivered over several weeks, is the traditional standard of care for low-risk breast cancer. More recently, hypofractionated, partial-breast irradiation has increasingly become established. Neoadjuvant single-fraction radiotherapy (rt) is an uncommon approach wherein the unresected lesion is irradiated preoperatively in a single fraction. We developed the signal (Stereotactic Image-Guided Neoadjuvant Ablative Radiation Then Lumpectomy) trial, a prospective single-arm trial to test our hypothesis that, for low-risk carcinoma of the breast, the preoperative single-fraction approach would be feasible and safe. Methods: Patients presenting with early-stage (T < 3 cm), estrogen-positive, clinically node-negative invasive carcinoma of the breast with tumours at least 2 cm away from skin and chest wall were enrolled. All patients received prone breast magnetic resonance imaging (mri) and prone computed tomography simulation. Treatable patients received a single 21 Gy fraction of external-beam rt (as volumetric-modulated arc therapy) to the primary lesion in the breast, followed by definitive surgery 1 week later. The primary endpoints at 3 weeks, 6 months, and 1 year were toxicity and cosmesis (that is, safety) and feasibility (defined as the proportion of mri-appropriate patients receiving rt). Results: Of 52 patients accrued, 27 were successfully treated. The initial dosimetric constraints resulted in a feasibility failure, because only 57% of eligible patients were successfully treated. Revised dosimetric constraints were developed, after which 100% of patients meeting mri criteria were treated according to protocol. At 3 weeks, 6 months, and 1 year after the operation, toxicity, patient- and physician-rated cosmesis, and quality of life were not significantly different from baseline. Conclusions: The signal trial presents a feasible method of implementing single-dose preoperative rt in early-stage breast cancer. This pilot study did not identify any significant toxicity and demonstrated excellent cosmetic and quality-of-life outcomes. Future randomized multi-arm studies are required to corroborate these findings.