IORT for early-stage, low-risk breast cancer: Outcomes from a prospective, observational study

Treatment of early-stage, low-risk breast cancer (BC) has undergone significant de-escalation during the past years. The TARGIT-A trial provided information on intraoperative radiotherapy (IORT) as a convenient, single-fraction modality. Nevertheless, significant discussion regarding different aspects of the trial continues. This study reports on oncological outcomes in a real-world clinical setting and contributes to the understanding of its optimal indication.

Five-hundred patients planned for breast-conserving surgery (BCS) were screened for IORT between June 2017 and December 2023, within this prospective, observational, single-center. The treatment protocol replicated the experimental arm of the TARGIT-A trial, implementing stricter inclusion criteria and maintaining a risk-adapted approach. The primary endpoint was ipsilateral breast recurrence rates (IBR). Secondary endpoints included local recurrence-free survival, progression-free survival, overall survival, and patient-reported cosmesis. The Kaplan-Meier method was used to analyze survival and recurrence risk, and risk factors for IBR were assessed through Cox regression analysis.

After screening and recruiting, IORT was performed in 464 patients. The median follow-up was 45.3 (8-89) months. The estimated 5-year IBR risk in the entire cohort was 1.7 % (95 % CI: 0.7 %-2.8 %), decreasing to 1 % (95 % CI: 0.3 %-2.4 %) in the IORT + whole breast irradiation (WBI) cohort. In the IORT-only cohort, the risk was 2.1 % (95 % CI: 0.6 %-3.7 %). No significant differences were observed among the three subgroups. The 5-year overall survival and breast cancer-specific survival rates were 97.6 % (95 % CI: 96.0 %-99.1 %) and 99.5 % (95 % CI: 98.5 %-100 %), respectively. Two independent significant risk factors for IBR were identified: age < 50 years (HR = 0.138, 95 % CI: 0.032-0.597, p = 0.008) and close or affected surgical margins (HR = 5.8, 95 % CI: 1.5-22.5, p = 0.011). No grade 3-4 toxicity events were reported. Patient-reported cosmesis was excellent/good in 84 % of cases.

Local recurrence rates were low amongst all groups. Superior control outcomes could be obtained by applying more restrictive criteria than the TARGIT A trial. Longer follow-up is needed to confirm our findings.