To determine the patterns of failure and prognostic factors for locoregional recurrence after postmastectomy radiotherapy (RT), using a specific electron beam technique.

A uniform electron beam was used in 323 patients with invasive breast cancer at the University of Florida Health Science Center. The patterns of disease recurrence, prognostic factors, and overall outcome were studied.

At 10 years, the freedom from locoregional recurrence, disease-free survival, and absolute survival rate was 90%, 62%, and 55%, respectively. The 10-year disease-free survival rate for patients with 0, 1-3, and >3 positive lymph nodes was 73%, 75%, and 47%, respectively. On multivariate analysis, the three factors significantly associated with locoregional recurrence were T stage, number of involved nodes, and RT fields. Full axillary fields appeared to be beneficial (p = 0.02). Patients with positive surgical margins appeared to benefit from a mastectomy incision boost to >/=65 Gy. Finally, patients with T2N0 disease had a substantial risk of chest wall recurrence without chest wall RT.

Findings include a low rate of clinically detectable locoregional recurrence. The data suggest benefits for the addition of full axillary RT in node-positive patients and chest wall RT in patients with T2N0 disease.