Outcomes in ER-negative Breast Cancer Treated with Accelerated Partial Breast Irradiation Using Intracavitary Brachytherapy

Abstract

The American Brachytherapy Society (ABS), American Society for Therapeutic Radiology and Oncology (ASTRO), and European Society for Therapeutic Radiology and Oncology (ESTRO) have conflicting recommendations regarding the treatment of estrogen receptor (ER)-negative breast tumors with accelerated partial breast irradiation (APBI). The purpose of this study was to evaluate these 3 guidelines using a single institutional experience with treating ER-negative breast cancer with APBI. This is a single institution retrospective review of 76 consecutive patients with biopsy confirmed breast cancer who underwent lumpectomy followed by APBI intracavitary brachytherapy to a dose of 34.0 Gy in 10 fractions from 2003-2018. Patient demographics, tumor/treatment details, and outcomes were abstracted from the electronic medical record. Outcomes, including recurrence-free survival (RFS), ipsilateral breast tumor recurrence (IBTR), contralateral breast tumor recurrence (CBTR), distant metastasis (DM), and overall survival (OS) were estimated with Kaplan-Meier univariate analysis (UVA). Median follow-up time for all patients was 60.2 months (range 0-141 months). The median age at time of treatment was 69 years (range 50-86 years). There were 18 cases of DCIS, 53 cases of IDC, 3 cases of adenoid cystic carcinoma, 1 case of apocrine carcinoma, and 1 case of ILC. There were 56 patients with triple negative breast cancer, 9 patients with PR-positive disease, and 12 patients with HER2-positive disease. There were 8, 16, and 52 cases of grade 1, 2, and 3 disease, respectively. The majority of patients had pN0 disease (63 cases), while the remaining 13 cases, all of which DCIS, did not undergo lymph node evaluation (pNX). Amongst those with DCIS with adequate clinicopathologic data (N = 15), 9 were deemed suitable by ABS criteria, all were deemed cautionary by ASTRO criteria, and all were deemed intermediate risk by ESTRO criteria. Of the evaluable patients with invasive cancer (N = 54), 48 were deemed suitable by ABS criteria, all were deemed cautionary by ASTRO criteria, and 33 were deemed low risk by ESTRO criteria. Twenty-seven patients (35.5%) received adjuvant chemotherapy while 11.8% of patients received endocrine therapy. There was one case of IBTR and no cases of CBTR or DM. Five-year OS, RFS, IBTR, and DM were 88.5%, 98.4%, 1.6%, and 0%, respectively. These results demonstrate the efficacy of intracavitary brachytherapy APBI in patients with early stage, locally controlled ER-negative breast cancer. In light of these results, and given that current guidelines deem ER-negative breast cancer tumors as cautionary or unsuitable for APBI, consideration should be made to expand the current eligibility criteria for treatment of ER-negative breast cancer with APBI using intracavitary brachytherapy.