ESTRO 2025 - Abstract Book

S3916

Radiobiology - Normal tissue radiobiology

ESTRO 2025

1443

Poster Discussion Molecular validation of a non-coding single-nucleotide polymorphism associated with the risk of radiation induced fibrosis Ahmad Sami 1,2 , Carsten Sticht 3 , Carsten Herskind 1,2 1 Department of Radiation Oncology, Universitätsmedizin Mannheim, Medical Faculty Mannheim, Heidelberg University, Mannheim, Germany. 2 *, DKFZ-Hector Cancer Institute at University Medicine Mannheim, Mannheim, Germany. 3 NGS Core Facility, Medical Faculty Mannheim, Heidelberg University, Mannheim, Germany Purpose/Objective: While developing a predictive model for skin fibrosis after radiotherapy for breast cancer, we identified a non coding candidate SNP associated with reduced risk within a subgroup of patients with an increased risk according to the functional RILA assay ([1] and Sami et al., in preparation). The SNP is located downstream of a gene related to the extracellular matrix (ECM) but its biological function remains poorly understood. The purpose of the present work was to study its functional impact at the transcriptional level. Material/Methods: Patient-derived dermal fibroblasts from a local biobank were previously genotyped for the candidate SNP (its identity will be revealed at the ESTRO meeting). Six fibroblast strains from each of the major homozygotes (CC), heterozygotes (CT), and minor homozygotes (TT), were cultured to passage 6 and irradiated with 4Gy or sham irradiation. Total cellular RNA, used for gene expression quantification by RNA-seq, was collected before irradiation and on day-2 post-treatment. After trimming low-quality reads (Trimmomatic), Kallisto software was employed for pseudo-alignment and read counting. Data normalisation and differential gene expression (DGE) analysis were performed with the limma package (FDR<0.05), with pathway enrichment analysis carried out using the ReactomePA package in R. Results: The basal expression levels (day-0) showed few significant differentially expressed genes (DEGs) between the genotypes (TT vs CC: n=5; TT vs CT: n=2; CT vs CC: n=1). Transcriptome changes two days after treatment were assessed by comparing day-2 samples for each genotype to the untreated CC genotype as a common control (day 0). A significantly different number of DEGs were observed in fibroblasts with the different genotypes, in both irradiated and untreated samples (p<0.001, Chi-squared test). Fibroblasts with the CC genotype showed the highest number of DEGs on day-2 (0Gy n=2372, 4Gy n=9576). Fibroblasts with TT genotype showed significantly smaller numbers of DEGs (0Gy n=523, 4Gy n=3538) while CT fibroblasts being intermediate (0Gy n=788, 4Gy n=5471). Pathway analysis after irradiation showed similar expected responses across all three genotypes, as previously published (2). However, pathways involved in cell-cycle regulation, metabolism, and signal transduction were underrepresented in TT fibroblasts at baseline but overrepresented on day-2 post-irradiation, compared to CC fibroblasts. Analysis of leading-edge genes revealed that distinct genes were responsible for these under- and over representation, respectively. Conclusion: This study demonstrates that the candidate SNP influences fibroblast irradiation response, primarily affecting biological pathways related to growth and stress regulation. These findings may guide personalised approaches to fibrosis risk management.

Keywords: fibrosis, RNA-seq, SNP

References: 1.

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