No increased risk for accelerated partial breast irradiation with multicatheter brachytherapy in early-stage invasive lobular carcinoma

Purpose
To analyze the oncological outcomes of adjuvant accelerated partial breast irradiation (APBI) delivered via multicatheter interstitial high-dose-rate (HDR) brachytherapy in patients with early-stage invasive lobular carcinoma (ILC) following breast-conserving surgery (BCS).

Material and methods
We retrospectively reviewed our institutional database to identify patients with pure or mixed ILC histology, treated with BCS followed by adjuvant APBI by multicatheter brachytherapy. Patients were selected for APBI according to the Groupe Européen de Curiethérapie-European Society for Radiotherapy and Oncology (GEC-ESTRO) recommendations. Ipsilateral breast tumor recurrence (IBTR) and overall survival (OS) were estimated using Kaplan-Meier method.

Results
Forty-seven patients with ILC treated between February 2016 and March 2023 were included. Pre-operative breast magnetic resonance imaging (MRI) was performed in 37 patients (78.7%). The median age was 65 years (range, 49-80 years), and the median tumor diameter was 1.1 cm (range, 0-2.5 cm). Forty-four patients (93.6%) met all low-risk criteria; 3 patients (6.4%) were included despite the presence of lymphovascular space invasion (LVSI). Treatment consisted of 32 Gy in 8 fractions for 44 patients (93.6%), and 30.1 Gy in 7 fractions for 3 patients (6.4%). Adjuvant anti-hormonal therapy was given to 42 patients (89.4%). At a median follow-up of 47 months (range, 24-106 months), no IBTR was observed. One non-breast cancer-related death occurred, resulting in a 4-year OS of 97%. Late side effects included mild hyperpigmentation in 2 patients (4.3%) and breast asymmetry in 1 patient (2.1%). Asymptomatic fatty tissue necrosis was detected in 7 patients (14.9%) during follow-up mammography.

Conclusions
APBI delivered via multicatheter brachytherapy for early-stage ILC appears to be a safe treatment modality, and it was not associated with an increased risk of ipsilateral breast tumor recurrence in this cohort.