Salvage Breast-Conserving Surgery and Reirradiation With Intraoperative Electrons for Recurrent Breast Cancer: A Multicentric Study on Behalf of Italian Association of Radiotherapy and Clinical Oncology (AIRO).

Purpose: Intraoperative radiation therapy with electrons (IOERT) may represent a viable choice for partial breast reirradiation after repeat quadrantectomy for local recurrence (LR) for primary breast cancer (BC) in lieu of mastectomy.

Methods and materials: A database collecting data on partial breast reirradiation with IOERT from 8 Italian centers was set up in 2016 to 2018, providing data on cumulative incidence (CumI) of second LR and survival with a long follow-up.

Results: From 2002 to 2015, 109 patients underwent the conservative retreatment. The median primary BC first LR interval was 11.1 years (range, 2.4-27.7). The median first LR size was 0.9 cm (range, 0.3-3.0), and 43.6% cases were luminal A. Median IOERT dose was 18 Gy (range, 12-21), and median collimator diameter was 4 cm (range, 3-6). Median follow-up duration was 11.7 years (IQR, 7.7-14.6). The second LR CumI was 12.2% (95% CI, 6.8%-19.2%) at 5 years and 32.3% at 10 years (95% CI, 22.8%-42.2%), occurring in the same site as the first LR in about half of the cases. Human epidermal growth factor receptor 2 status and collimator size were independent LR predictors. The 5- and 10-year overall survival rates were 95.2% and 88.3%, respectively, whereas 5- and 10-year BC-specific survival rates were 98% and 94.5%, respectively. The development of a second LR significantly reduced BC-specific survival (hazard ratio, 9.40; P < .001). Grade ≥3 fibrosis rate was 18.9%. Patient-reported cosmesis was good/excellent in 59.7% of the cases.

Conclusions: Second LR CumI was within the range of the literature but higher than expected, opening questions on radiation field extension and fractionation schedule. Because a second LR worsened the outcome, salvage modality must be carefully planned.