Intraoperative radiation therapy delivered at the time of lumpectomy for treatment of early-stage breast cancer: Median five-year follow-up outcomes of the single-arm, prospective, multi-institution ExBRT trial

Background Intraoperative radiation therapy has shown potential in early-stage breast cancer treatment. The single-arm, prospective, multi-institution ExBRT trial was designed to improve the quality of evidence in patients treated with lumpectomy and intraoperative electronic brachytherapy (IORT). Methods Women at least 40 years with single lesion invasive ductal carcinoma (IDC) or ductal carcinoma in situ (DCIS) no larger than 3cm, cN0, treated with lumpectomy and IORT per protocol, were followed for ipsilateral breast tumor recurrence (IBTR), serious adverse events (SAEs), breast cancer-related and overall survival. Results At median 5-year follow-up, IBTR was diagnosed in 42(3.50%) of 1199 subjects, with a Kaplan-Meier probability of 4.21% (95%CI 2.86, 5.55). IBTR-related risk analyses identified age younger than 50 years, high-grade DCIS, Grade 3 IDC and endocrine therapy (ET) non-compliance to increase IBTR risk. SAEs were low at 1.4%. Breast cancer-related survival had a median 5-year Kaplan-Meier probability of 99.90% (95%CI 99.70, 100), with 1 breast cancer-related death. There were 46 unrelated deaths for an overall survival probability of 94.30% (95%CI 92.67, 95.95). Conclusions Patients treated with lumpectomy and IORT, delivered conveniently in a single setting, demonstrated low IBTR with minimal toxicity and excellent breast cancer-related and overall survival. This compared favorably to published early-stage breast cancer radiation omission and de-escalation radiotherapy results. Synopsis A single-arm, prospective, multi-institution research study (ExBRT trial) assessing IORT safety and efficacy immediately following lumpectomy using disposable balloon electronic brachytherapy. IORT, with a 4.21% Kaplan-Meier IBTR probability at median 5-year follow-up, is a convenient, less toxic treatment with results similar to early-stage breast cancer radiation omission and de-escalation radiotherapy results.