Accelerated Partial Breast Irradiation in Guideline-Defined Suitable and Cautionary Patients

Abstract

The 2016 ASTRO Consensus Guidelines for the use of accelerated partial breast irradiation (APBI) define “suitable”, “cautionary” and “unsuitable” populations for this adjuvant breast radiotherapy technique. We sought to determine whether patients in the “cautionary” group exhibited adverse outcomes in comparison to their “suitable” counterparts. We identified 252 consecutive patients from a single institution with in situ or early-stage invasive breast cancer that were treated with APBI from 2008 to 2017. Treatment technique was uniform throughout the population, consisting of 3D-conformal radiotherapy (3D-CRT) to 40 Gy administered in 10 daily fractions. One hundred seventy-eight patients (70.6%) were categorized as suitable, 71 (28.2%) as cautionary, and 3 (1.2%) as unsuitable. At a median follow-up of 3.5 years (range: 0.3-9.2), there was no significant difference in the rates of ipsilateral breast recurrence (1.4% vs 1.1%, P = 0.64) between cautionary and suitable groups. Characteristics significantly associated with cautionary patients compared to suitable patients included close margins (defined as <2mm for invasive cancer and <3mm for in situ ; 23.6% vs. 0%, P <0.001), invasive lobular histology (12.7% vs. 0%, P <0.001), lack of estrogen receptor expression (11.3% vs. 0%, P <0.001), lymphovascular invasion (8.5% vs. 0%, P <0.001), and age (average 61 vs. 63, P = 0.04). The groups did not differ significantly with respect to tumor size, histologic grade, HER2 expression, or treatment with either chemotherapy or hormone therapy. Young age was the most common cautionary feature (32.4% of patients in the cautionary group <50 years old), followed by close margin status (23.9% of patients in the cautionary group). A total of 11.3% of patients in the cautionary group had >1 “cautionary” risk factor. Local recurrences are rare among guideline-defined “cautionary” patients with in situ or invasive breast cancer treated with APBI delivered via daily 3D-CRT to 40Gy. At a median follow-up of 3.5 years, no significant differences in local control were noted between cautionary and suitable patient groups. Longer-term follow-up is needed to fully characterize the safety and feasibility of APBI in this group.