Five‐year outcome of patients classified using the American Society for Radiation Oncology consensus statement guidelines for the application of accelerated partial breast irradiation

Abstract

Purpose/Objective(s): The ASTRO consensus statement (CS) for the application of accelerated partial breast irradiation (APBI) was applied to patients treated with this technique on the American Society of Breast Surgeons (ASBS) MammoSite Registry Trial to determine potential differences in clinical outcome based upon classification group. Materials/Methods: Patients were classified based on the CS groups of “suitable,” “cautionary,” and “unsuitable.” Rates of ipsilateral breast tumor recurrence (IBTR), regional nodal failure (RNF), distant metastases (DM), disease-free survival (DFS), cause-specific survival (CSS), and overall survival (OS) were assessed. Results: Of the 1,449 cases treated, 1,025 (71%) could be classified according to the CS groupings, of which 419 (41%) fit the “suitable” criteria, 430 (42%) the “cautionary” criteria, and 176 (17%) the “unsuitable” criteria. At a median follow-up of 53.5 months, the five-year actuarial rates of IBTR for the “suitable,” “cautionary,” and “unsuitable” groups were as follows: 2.59%, 5.43%, and 5.28%, respectively (p = 0.1884). Univariate analysis of factors potentially associated with IBTR found estrogen receptor negative status to be the only variable associated with IBTR among patients with invasive breast cancer (OR 4.01, p = 0.0003). Larger tumor size was associated with a greater risk of DM (OR 3.05, p = 0.0001). Among patients with ductal carcinoma in situ, only age <50 years and close-positive margins were associated with IBTR (OR 1.12, p = 0.0079 and OR 7.81, p = 0.0131, respectively). Conclusions: The ASTRO CS groupings did not differentiate a subset of patients with a significantly worse rate of IBTR when treated with the MammoSite® breast brachytherapy catheter to deliver APBI.