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Background/Aims: Due to its favorable dose distribution and targeting of the region at highest risk of recurrence due to direct visualization of tumor bed, intraoperative electron radiation therapy (IOERT) is used as part of a breast-conserving treatment approach. The aim of this study was to analyze tumor control and survival, as well as the toxicity profile, and cosmetic outcomes in patients irradiated with an IOERT boost for breast cancer. Materials and Methods: 139 Patients treated at our institution between January 2010 and January 2015 with a single boost dose of 10 Gy to the tumor bed during breast-conserving surgery followed by whole-breast irradiation were retrospectively analyzed. Results: 139 patients were included in this analysis. The median age was 54 years (range 28–83 years). The preferred surgical strategy was segmental resection with sentinel lymphonodectomy (66.5%) or axillary dissection (23.1%). Regarding adjuvant radiotherapy, the vast majority received 5 × 1.8 Gy to 50.4 Gy. At a median follow-up of 33.6 months, recurrence-free and overall survival were 95.5% and 94.9%, respectively. No patient developed an in-field recurrence. Seven patients (5.0%) died during the follow-up period, including two patients due to disease recurrence (non-in-field). High-grade (CTCAE > 2) perioperative adverse events attributable to IOERT included wound healing disorder (N = 1) and hematoma (N = 1). High-grade late adverse events (LENT-SOMA grade III) were reported only in one patient with fat necrosis. Low-grade late adverse events (LENT-SOMA grade I-II) included pain (18.0%), edema (10.5%), fibrosis (21%), telangiectasia (4.5%) and pigmentation change (23.0%). The mean breast retraction assessment score was 1.66 (0–6). Both patients and specialists rated the cosmetic result “excellent/good” in 84.8% and 87.9%, respectively. Conclusion: Our study reports favorable data on the cosmetic outcome as well as the acute and early long-term tolerability for patients treated with an IOERT boost. Our oncologic control rates are comparable to the previous literature. However, prospective investigations on the role of IOERT in comparison to other boost procedures would be desirable.

Neoadjuvant chemotherapy enables close monitoring of tumor response in patients with breast cancer. Being able to assess tumor response during treatment provides an opportunity to evaluate new therapeutic strategies. Thus, for triple-negative breast tumors, it was demonstrated that additional immunotherapy could improve prognosis compared with chemotherapy alone. Furthermore, adjuvant therapy can be escalated or de-escalated correspondingly. The CREATE-X trial randomly assigned HER2-negative patients with residual tumor after neoadjuvant therapy to either observation or capecitabine. In HER2-negative patients with positive BRCA testing, the OlympiA study randomly assigned patients to either observation or olaparib. HER2-positive patients without pathologic remission were randomly assigned to trastuzumab or trastuzumab–emtansine within the KATHERINE study. These studies were all able to show an improvement in oncologic outcome associated with the escalation of therapy in patients presenting with residual tumor after neoadjuvant treatment. On the other hand, this individualization of therapy may also offer the possibility to de-escalate treatment, and thereby reduce morbidity. Among WSG-ADAPT HER2+/HR-, HER2-positive patients achieved comparable results without chemotherapy after complete remission following neoadjuvant treatment. In summary, the concept of post-neoadjuvant therapy constitutes a great opportunity for individualized cancer treatment, potentially improving outcome. In this review, the most important trials of post-neoadjuvant therapy are compiled and discussed.