ESTRO 2021 Abstract Book

S37

ESTRO 2021

The TCGA analysis revealed markedly higher expression of the CAF associated markers FAP, Thy1/CD90, PDGFRβ and TGFβ3 in HNSC samples compared to normal tissue samples ( Figure 1A ). Microscopy analyses showed that irradiation dose-dependently increases the cell area of CAFs derived from all four different xenografts ( figure 1B ). Moreover, expression of several CAF associated (alphaSMA, Podoplanin, FSP1/S100A4, Thy1/CD90 and CD29/β1-integrin) and immunomodulatory markers (MHCII, CD86 and PD-L1) was dose- dependently upregulated upon irradiation ( Figure 1C-E ).

Conclusion Our data suggest increased presence of CAFs in HNSC tissues compared to normal tissue, suggesting that CAFs may contribute to the malignant phenotype and/or tumorigenesis of HNSCC. In addition we show that irradiation has a major impact on the phenotype of HNSCC-derived CAFs. It affects their morphology as well as the expression of markers that are important in steering anti-tumor (immune) responses. It may therefore also potentially affect the efficacy of future immunotherapy. Current research focuses on the effect of RT on the function and heterogeneity of CAFs in vivo and the subsequent effect on modulating the anti-tumour immune response and efficacy of immunotherapy. More knowledge regarding the function of CAFs and how they are affected by RT in the TME of HNSCC may ultimately benefit the rational design of cancer therapy. OC-0062 Potential predictive biomarkers for Nimorazole-modified radiochemotherapy in head and neck cancer M.J. Besso 1 , V. Bitto 1 , L. Koi 2,3,4 , W. Hadiwikarta 1 , R. Euler-Lange 5 , M. Bonrouhi 1 , A. Linge 2,3,6,7 , M. Krause 2,3,8,9,10 , I. Kurth 1 , M. Baumann 1,11,12 1 German Cancer Research Center (DKFZ), Radiooncology/Radiobiology, Heidelberg, Germany; 2 OncoRay – National Center for Radiation Research in Oncology, Faculty of Medicine and University Hospital Carl Gustav Carus, Technische Universität Dresden, Helmholtz-Zentrum Dresden - Rossendorf, Dresden, Germany; 3 Department of Radiotherapy and Radiation Oncology, Faculty of Medicine and University Hospital Carl Gustav Carus, Technische Universität Dresden, Dresden, Germany; 4 Helmholtz-Zentrum Dresden - Rossendorf,