ESTRO 2024 - Abstract Book

S5387

Radiobiology - Tumour biology

ESTRO 2024

immune-related biomarkers. Image acquisition was performed using the Leica BOND-MAX™ automated system. Staining intensity for immune biomarkers was evaluated independently by at least three researchers and given a score of 0, 1 or 2 for negative, low or high signal intensity respectively. For the transcriptome analysis, total RNA was extracted from frozen pre-treatment samples using PureLink RNA mini isolation kit. Samples quality was evaluated with Nanodrop and RNA sequencing was performed at Lexogen by using a total of 10 ng/uL. The statistical analyses aiming at detecting differences in gene expression according to tumor downstaging were conducted by fitting age adjusted linear regression models, and applying the false discovery rate (FDR) method for correcting for multiple tests. We then performed enrichment analysis by using the DeSeq2 and ClusterProfiler packages in R.

Results:

Patients underwent breast surgery 2 to 4 weeks after radiosurgery. Of the 22 treated patients, tumor downstaging after prRS was evaluated at the time of surgery according to pTNM: 8 patients with tumor downstaging were classified as Radio-Responders (R-R) and 13 patients were classified as no-Radio-Responders (NR-R). RNAseq analysis showed 100 genes differentially expressed with p value < 0.05 between R-R and NR-R. After FDR correction for multiple testing, only CCDC97 gene remained significantly increased in R-R patients (p=0,0082) (fig 1 Volcano plot). CCDC97 is an orphan gene, previously described as part of a nuclear interactome with functional role in DNA damage repair (ref 1). Gene set enrichment analysis (GSEA) revealed that p53-related signaling and cellular response to radiation and DNA damage-related pathways were over-represented, but no significant association after FDR correction for multiple testing was observed. IHC was performed on available 19 pairs of pre-irradiation and post-irradiation tissue for immune-related biomarkers evaluation. CD68, CD163, CD4, CD8, CD56, CD16, and FOXP3 were analyzed, and immune infiltrate of each patient was compared before/after irradiation; preliminary analysis showed an increase of CD8+ cells and CD16+ cells in R-R patients after prRS.