ESTRO 2020 Abstract book

S1063 ESTRO 2020

without changes in MDSCs. This treatment modality may be an effective approach to improve antitumor immunity, which is a relevant finding for supporting future combinations of IORT with immunotherapy for treating breast cancer patients. PO‐1813 Plasma biomarkers of immunogenic cell death during and after SBRT and concurrent chemo‐RT for NSCLC. K. Reynders 1,2 , A.D. Garg 3 , E. Van Limbergen 1 , P. Agostinis 3 , J. Vansteenkiste 4 , L. Hendriks 5 , K. Rouschop 6 , Developmental Biology- Maastricht University Medical Centre+, Department of Radiation Oncology, Maastricht, The Netherlands ; 2 KU Leuven, Laboratory of Experimental Radiation Oncology, Leuven, Belgium ; 3 KU Leuven, Laboratory for Cell Death Research and Therapy CDRT- Department of Cellular and Molecular Medicine, Leuven, Belgium ; 4 University Hospitals KU Leuven, Respiratory Oncology Unit, Leuven, Belgium ; 5 GROW School for Oncology and Developmental Biology- Maastricht University Medical Centre+, Department of Pulmonary Diseases, Maastricht, The Netherlands ; 6 MAASTRO- GROW School for Oncology and Developmental Biology- Maastricht University Medical Centre+, Maastricht Radiation Oncology Lab, Maastricht, The Netherlands ; 7 Olink Proteomics, Scientific Advisor, Watertown- MA, USA ; 8 University Hospitals KU Leuven, Department of Radiation Oncology, Leuven, Belgium Purpose or Objective Radiotherapy (RT) is capable of inducing pro-immunogenic cell death (ICD), antigen upregulation and T-cell attraction. To the best of our knowledge, no data are available on the expression and evolution of ICD markers during RT for non-small cell lung cancer (NSCLC). In this exploratory, prospective study, we investigated a set of comprehensive ICD markers at different time points during RT. Material and Methods Patients with newly diagnosed NSCLC scheduled to receive stereotactic body radiotherapy (SBRT) for stage I disease or concurrent radiotherapy (≥ 60 Gy/2Gy) and cisplatin- doublet chemotherapy (CRT) for stage III were included. Excluded were chronic corticosteroid or NSAID use, active auto-immune diseases or immunosuppressive medication. Plasma samples were collected at three time points: immediately before treatment, before the second/third fraction for SBRT or CRT, respectively, and immediately after the last or second last fraction for SBRT or CRT, respectively. Comprehensive proteomic analysis was performed using a multiplex proximity extension assay that enabled detection of more than 1000 proteins simultaneously. A linear mixed model with maximum likelihood estimation for model parameters was used to detect proteins with an average concentration change of at least 50% from baseline to subsequent time points and to analyze differences between treatment groups. Significant differences were determined after Benjamini and Hochberg multiple hypothesis correction. A Kyoto Encyclopedia of Genes and Genomes (KEGG) mapping to look for differences in protein relation networks between the time points was done. The trial was approved by the ethics committees and listed under clinical trial number: NCT02921854. Results 128 plasma samples were collected from 47 patients (26 SBRT, 21 CRT). 36 proteins showed an altered protein expression which differed at least 50% from baseline; 2 in the SBRT group and 34 in the CRT group. In the SBRT group, NCF2 and NMNAT1 proteins, both involved in superoxide production, were increased at time point 2. In the CRT group, the most notable results were an increase in proteins involved in T-cell immunity (IFN-γ, CCL17, M. Rucevic 7 , M. Lambrecht 8 , D. De Ruysscher 1 1 MAASTRO- GROW School for Oncology and

Results For a total of 127 patients median age was 61 years. 54% were male and 72% of the tumors were localized in the parotid gland. Of the 13 occurring tumor histologies within this cohort, the three most frequent were adenocarcinoma (NOS, 24%), adenoid cystic carcinoma (19%) and mucoepidermoid carcinoma (17%). High overall CD8+ and PD-L1 tumor infiltration was associated with higher age (p=0.016, p=0.040) and the histological tumor subtype (p=0.005, p=0.046). Overall high CD8+ infiltration (OS: p=0.046) and high CD8+ infiltration of the tumor invasive front (OS: p<0.001, PFS: p=0.033) correlated with impaired outcome. For PD-L1, positive staining of ≥5% of the tumor cells was associated with worse OS (p=0.002). Regarding combined CD8+/PD-L1 expression, patients with low overall CD8+ infiltration showed better OS, regardless their PD-L1 status (p=0.004). Conclusion SGC are a heterogeneous group of carcinomas with varying immune infiltration and prognosis. In this retrospective cohort high CD8+ tumor infiltration and high PD-L1 expression were associated with impaired overall survival. These results should be validated in a multicentric cohort. PO‐1812 Peripheral immune cells and intraoperative radiation in low‐risk breast cancer I. Linares 1 , M.A. Berenguer Frances 1 , R. Cañas-Cortés 2 , M. Pujol-Canadell 2 , M. Nuñez 1 , S. Comas Antón 3 , E. Martinez 4 , M. Laplana 4 , H. Pérez-Montero 4 , M.J. Pla Farnós 5 , B. Both 6 , F. Guedea 1 1 Institut Català d´Oncologia. Institut d’Investigació Biomèdica de Bellvitge IDIBELL, Radiation Oncology. Radiobiology and Cancer Group- ONCOBELL Program, Barcelona, Spain ; 2 Institut d’Investigació Biomèdica de Bellvitge IDIBELL, Radiobiology and Cancer Group- ONCOBELL Program, Barcelona, Spain ; 3 Hospital Germans Trias i Pujol, Radiation Oncology, Badalona, Spain ; 4 Institut Català d´Oncologia, Radiation Oncology, Barcelona, Spain ; 5 Hospital Universitari de Bellvitge, Gynecology Department, Barcelona, Spain ; 6 Medical Technology Business Group- Carl Zeiss Meditec AG- ZEISS Group, Director Medical Affairs & Professional Education- Business Sector Radiotherapy, Oberkochen, Germany Purpose or Objective The purpose of this study was to assess changes in peripheral blood immune cell composition after intraoperative radiation therapy (IORT) on the surgical bed in low-risk breast cancer undergoing conserving breast surgery. Material and Methods Peripheral blood samples from 13 patients were collected preoperatively and at 48 hours and 3 and 10 weeks after IORT in a single dose of 20 Gy. Peripheral B lymphocytes, CD8+ cytotoxic T cells, CD4+ T helper cells, natural killer cells (NK), regulatory T cells (Treg), and myeloid-derived suppressor cells (MDSCs) were determined by flow cytometry. Results The subpopulation of NK CD56 +high CD16+ increased significantly at 3 weeks after IORT (0.30% to 0.42%, p < 0.001). Significant changes in the subpopulation of NK CD65-/CD16+ after treatment with IORT were observed throughout the study period (p = 0.05). There was an increase of CD8+ cytotoxic T cells, with the highest levels attained at 10 weeks after IORT (60.20% to 67.10%). A progressive decrease of Treg CD4+CD25+Foxp3+Helios subpopulation, with the lowest values at 3 weeks (38.50% to 27%, p = 0.454) was observed. Changes in MDSCs after IORT were not found (p = 0.11). Conclusion The administration of a single dose of IORT altered the balance of peripheral immune cells by increasing NK cells and cytotoxic T lymphocytes, while decreasing Treg cells