Oncological outcomes of breast cancer patients after planned IORT boost with low-kV x-rays-results of the TARGIT BQR prospective phase IV trial.

Purpose: The TARGIT BQR (boost quality registry) phase IV trial investigates clinical outcomes of breast cancer patients with standard external-beam radiotherapy (EBRT) of the whole breast and intraoperative radiotherapy (IORT) with low-kV x‑rays as an anticipated tumor bed boost in a real-world setting.

Methods: Intraoperative radiotherapy was performed immediately after breast-conserving surgery in one fraction. External-beam radiotherapy and systemic treatment were given according to the German S3 guideline for breast cancer and local tumor board recommendations. Outcome parameters were death, local recurrence, metastasis, local lymph node recurrence, and ipsilateral and contralateral invasive breast cancer. Kaplan-Meier estimates were used to calculate overall survival, metastasis-free survival, local recurrence-free survival, and disease-free survival.

Results: From 10 centers, 1133 patients were recruited. This analysis included 871 patients with 879 cancers, with a median follow-up of 36 months (up to 12 years). An IORT boost was performed in 82% and whole-breast irradiation in 84%. Overall survival was 98.4% after 3 years, 96.8% after 5 years, and 95.4% after 10 years (16 deaths; 1.8%). Metastasis and local recurrence occurred in 11 patients each (1.3%). At 5 years, the local control rate was 97.4% and local recurrence-free survival was 94.4%. Ipsilateral breast cancer occurred in 2 patients, contralateral breast cancer in 3 patients, and local lymph node recurrence in 2 patients. Disease-free survival was 92.9% after 5 years and 82.6% after 10 years.

Conclusion: This phase IV trial confirms previously reported outcomes on upfront IORT boost, with excellent disease-control outcomes.