ESTRO 2025 - Abstract Book

S1103

Clinical – Head & neck

ESTRO 2025

3861

Mini-Oral Radiotherapy-induced cGAS re-localization and immune signature as predictor for HNSCC treatment efficacy Vera Mekers, Paul Span, Maaike Looman, Lune van den Bogaard, Jan Bussink, Johannes Kaanders, Marleen Ansems, Gosse Adema Radiation Oncology, Radboudumc, Nijmegen, Netherlands Purpose and Objective Radiotherapy (RT) is an integral part of the treatment of head and neck squamous cell carcinoma (HNSCC) patients. Pre-clinical studies show RT-induced DNA damage activates the cyclic GMP-AMP-synthase (cGAS)/Stimulator of Interferon Genes (STING) pathway, underscoring the potential of combining RT with immunotherapy to achieve systemic effects (1,2). However, many questions linking RT and immune activation in clinical settings remain. Here we studied the cGAS-STING pathway in a unique set of HNSCC patient pre- and post (5x2 Gy) RT tumor biopsies and blood samples from the so-called “Second Biopsy study” Fig 1A). Materials & Methods We analyzed serial HNSCC tumor biopsies and blood samples to study RT-induced cGAS re-localization/activation. Pre- and post-RT tumor biopsies (fig 1A) were characterized by immunohstochemistry for the presence and localization of cGAS in tumor cells and immune cells. Interferon-stimulated gene (ISG) induction was determined by RNA expression profiling. Serum samples were tested in the serum-functional immunodynamics status (sFIS) assay (3) to assess RT-induced serum changes and the results were subsequently linked to clinical data. Results: We observed cGAS re-localization to micronuclei and ISG-induction post-RT in human HNSCC cell lines in vitro and in tumor biopsies from HNSCC patients after 1 week of daily 2Gy RT (fig 1 B). Interestingly, cGAS-positive micronuclei were increased most notably after RT within immune cell-infiltrated tumor areas (Fig 1 C-G). Local ISG expression post-RT increased only in a subset of patients (Fig 2). Patients showing potent induction of systemic type I interferon levels in serum samples post-RT exhibited improved survival (Fig 2).