Intraoperative radiation therapy versus partial breast irradiation for early-stage breast cancer: A global, propensity-matched retrospective cohort study.

e12530 Background: Intraoperative radiation therapy (IORT) and partial breast irradiation (PBI) are two modalities of radiation used in the treatment of breast cancer. While PBI is delivered as multiple fractionated doses over several days, IORT is administered as a single dose during surgery. IORT may therefore improve patient comfort and convenience, though some studies have shown higher rates of locoregional recurrence compared to PBI. In 2023, a clinical practice guideline from the American Society of Radiation Oncology (ASTRO) was updated to exclude IORT from the treatment of early-stage invasive breast cancer or DCIS. However, real-world data directly comparing long-term outcomes between IORT and PBI is lacking. Here we present a retrospective database analysis comparing mortality and metastatic disease to the bone, liver, lung, and brain between patients with breast cancer treated with IORT versus PBI. Methods: This global population-based retrospective cohort study was designed utilizing the TriNetX Research network as the source of patient data and following STROBE (Strengthening the Reporting of Observational Studies in Epidemiology) guidelines. Two patient cohorts were created by utilizing ICD-10 and CPT codes. Two patient cohorts were created, both of whom had malignant neoplasm of the breast (C50). One received treatment with IORT (77424, 77425, or 77469) while the other had PBI (19296, 19297, or 19298). The cohorts were balanced for age, race, and ethnicity by propensity score matching and the greedy nearest neighbor algorithm, resulting in 686 patients in each arm. They were then compared for the five-year outcomes of overall mortality and development of metastatic disease to bone, liver, lung, and brain. Results: Five-year overall mortality for IORT was statistically similar to that of partial breast irradiation (4.7% vs 3.5%, RR 1.3, 95% CI (0.79,2.24), P value 0.28). The outcomes for distant metastatic disease were also statistically similar (2.9% vs 1.6%, RR 1.8, 95% CI (0.88,3.77), P value 0.10). Conclusions: These results indicate that IORT and PBI confer similar rates of five-year mortality and distant metastatic disease among patients with breast cancer. Limitations of this study include that we were not able to control for breast cancer diameter, molecular profile, or the particular modality of PBI used. Future prospective studies accounting for these factors can help to confirm the results seen here. Shared decision-making and careful patient selection are essential when choosing a modality of breast radiation treatment.