Postmastectomy chest wall radiotherapy with single low-energy electron beam: An assessment of outcome and prognostic factors

Abstract

This study aimed to evaluate the outcome of patients who had received postmastectomy chest wall radiotherapy using a single electron beam, and to identify the relevant factors that influenced prognosis. The medical records of patients with breast cancer treated with postmastectomy radiotherapy from January 2000 to December 2004 were retrospectively analyzed (n = 328). Two hundred seventy-one (82.6%) patients were staged as (tumor-nodes-metastasis [TNM]) T3-4, any N, M0; or T1-2, N2-3, M0, and 57 (17.4%) patients were staged as T1-2, N1, M0. All patients received chest wall radiation with a 6-10 MeV electron beam. In addition, 327 patients (99.7%) received supraclavicular node radiation, 67 (20.4%) axillary radiation, and 35 (10.7%) internal mammary chain (IMC) radiation. Chemotherapy with anthracycline and taxane was given to 323 patients (98.5%). Of patients with positive hormone receptor, 183 (82.8%) received hormone therapy and 8 patients with negative and 3 patients with unknown hormone receptor received hormone therapy. Locoregional recurrence (LRR), distant metastasis (DM), and overall survival (OS) were calculated using the Kaplan-Meier method, and the differences assessed by log-rank test. The median follow-up time was 78 months (range, 5-123 months) for patients who remained alive. The 5-year LRR, DM, disease-free survival and OS rates were 5.9%, 26.2%, 72.5%, and 83.1%, respectively. LRR occurred in 1 or more sites in 21 patients. The 5-year recurrence rates in the chest wall, supraclavicular node, axilla, and internal mammary chain were 1.9%, 2.3%, 2.9%, and 0%, respectively. In multivariate analysis, hormone therapy was the only independent favorable prognostic factor for LRR (P = .017). LRR was significantly associated with DM and OS. The 5-year DM rate was 82.9% and 22.7% (P < .0001) and the 5-year OS rate was 52.8% and 84.7% (P < .0001) for patients with or without LRR. The treatment-related toxicity was low, with the incidence of symptomatic pneumonitis being 0.3%. Breast cancer patients can be treated with postmastectomy single electron beam radiotherapy with excellent local control and low toxicity.