S217
Clinical - Breast
ESTRO 2026
outcomes. We present our preliminary results. Material/Methods: This is a prospective, multicentre, phase II trial conducted at three Canadian institutions. Eligible participants are women ≥ 50 years, postmenopausal, with unifocal invasive ductal carcinoma ≤ 2 cm, estrogen receptor–positive ( ≥ 20%), HER2-negative, node-negative, and an Oncotype DX score ≤ 18 on biopsy sample. All patients received image-guided single-fraction partial breast external beam radiotherapy of 20 Gy. Hormone therapy began within 3 months post-RT. Surgery was scheduled 12 months after RT. Women aged ≥ 70 years achieving complete radiologic response on ultrasound at 12 months could elect to omit surgery. Results: Of 29 enrolled patients (30 lesions; one patient with bilateral disease), median age was 70 years (range 55- 86). At data cutoff, 17 patients completed the 12- month assessment, while 12 have not reached this time point. All 17 evaluable patients demonstrated clinical response at 12-months; 8 (47%) achieved complete radiological response by ultrasound. Ten patients underwent surgery. All surgical specimens showed marked pathological response with median residual cellularity of 1% (range 0-10%); with one patient (10%) achieved pathological complete response (0% viable tumour). Seven patients aged ≥ 70 years elected to omit surgery per protocol; median follow-up in that group is 19 months (range 16-30 months) compared to 17 months in the study population. There was no disease progression or recurrence in the no surgery group, and no recurrences in the study population. Treatment was well-tolerated: grade 1 dermatitis (n=1), grade 1 induration (n=3), grade 2 pain (n=3); no grade ≥ 3 toxicity occurred. Conclusion: SPORT-DNS is the first trial exploring the potential of single-dose radiotherapy as definitive local therapy in biologically favourable breast cancer. Both clinical and pathological response rates were very high, with no progressions or recurrences observed to date. Toxicity profile was excellent, especially in patients not undergoing surgery. Patient accrual is continuing, and longer follow-up is needed to confirm the safety of surgery omission; however these preliminary results support completion of this study and development of a phase III randomized trial to establish a new, less invasive paradigm for selected low-risk patients. Keywords: SBRT, non-operative management, early- stage
One post-surgical complication (liponecrosis) was registered, for which the role of preoperative RT remains to be established. During follow-up 1 patient developed a regional relapse and 2 patients a non- breast second primary. At a median follow-up of 22.12 months (range 7.5-43 months), all patients are alive with no evidence of disease.
Conclusion: Updated results confirm the feasibility and safety of preoperative single-fraction APBI delivered with CyberKnife in early-stage BC. Ongoing enrollement and longer follow-up will further define the clinical role of this innovative approach. Keywords: radioablation, preoperative, APBI Poster Discussion 741 A future without surgery? Single-fraction preoperative radiotherapy with delayed or no surgery in low-risk breast cancer: The phase II SPORT-DNS trial Tarek Hijal 1 , Jean-Marc Bourque 2 , Peter Vavassis 3 , Christine Lambert 1 , Lucas Sideris 4 , Sarkis Meterissian 5 , Kerianne Boulva 6 , Anne-Marie Charpentier 2 , Erica Patocskai 6 , Michael Yassa 3 1 Oncology, McGill University, Montreal, Canada. 2 Radiation Oncology, Centre hospitalier de l'Université de Montréal, Montreal, Canada. 3 Radiation Oncology, HMR - Hôpital Maisonneuve-Rosemont, Montreal, Canada. 4 Surgery, HMR - Hôpital Maisonneuve- Rosemont, Montreal, Canada. 5 Surgery, McGill University, Montreal, Canada. 6 Surgery, Centre hospitalier de l'Université de Montréal, Montreal, Canada Purpose/Objective: To evaluate the efficacy and safety of single-fraction preoperative radiotherapy followed by delayed surgery (vs observation) in postmenopausal women with low-risk early-stage breast cancer. The primary hypothesis is that neoadjuvant single-dose radiotherapy induces high rates of radiological and pathological complete response (pCR), potentially allowing selected patients with complete radiologic response to defer or omit surgery pending long-term
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