The purpose of this study was to evaluate local-regional control and overall survival in women with locally recurrent and metastatic breast cancer (MBC) treated with postmastectomy electron arc therapy. Postmastectomy electron arc irradiation was used to treat 39 women with isolated local-regional recurrence of breast cancer following mastectomy, and 14 patients with MBC who had, or who were at high risk of, local-regional recurrence. After computed tomography treatment planning, patients were treated with electron arc radiotherapy to a median dose of 59.3 Gy. The median follow-up for alive patients was 45.4 months. For patients with local-regional recurrence, the 5-year local-regional control and overall survival rates were 74% and 43%, respectively. The 2-year overall survival was greater for those patients with a disease-free interval greater than 24 months when compared to patients with a disease-free interval less than 24 months (83% vs. 60%, respectively); however, the median survival was not significantly different (57.6 and 58.6 months, respectively). Patients with a solitary nodule at recurrence had an improved 5-year overall survival of 58% compared with 40% for patients with multiple lesions. For patients with metastatic disease, the 5-year local-regional control and overall survival rates were 76% and 31%, respectively. Local-regional control can be achieved in the majority of patients with local-regionally recurrent breast cancer (74%) or MBC (76%) who had, or who were, at high risk of local-regional recurrence treated with postmastectomy electron arc irradiation.