S1462
Interdisciplinary - Other
ESTRO 2026
analysis." Advances in Neural Information Processing Systems 2024.[4] Xu et al. "Predicting axillary lymph node metastasis in early breast cancer using deep learning on primary tumor biopsy slides." Frontiers in oncology 2021.[5] Maynard et al. "Transcriptome-scale spatial gene expression in the human dorsolateral prefrontal cortex." Nature neuroscience 2021. Keywords: Tumor microenvironment, Precision radiotherapy
(DN) CD4/CD8 CD56-, NK, NK-like T cells with PD1 expression were defined by flow cytometry. cEVs were isolated from serum and analyzed for concentration, size and PD-L1 expression by nanoparticle tracking analysis and flow cytometry. The rate of pathological response on surgical specimens in terms of Mandart - TRG was acquired and compared with data of immunophenotype and cEVs. Results: In all surgical specimens a tumor downstage was recorded in terms of TRG 0-2. From T0 to T1, the median percentage of T lymphocytes decreased (68 vs 64%) in terms of T helper ( 47.9 vs 44.7%) and CD3+ DN CD4/CD8 CD56- (0.68 vs 0.56%). A major reduction was evident for B cells (4.6 vs 2.9 %). T helper PD1+, T reg PD1+ and NK increased (12.6 vs 15.3; 0.47 vs 0.87; 25 vs 32 %, respectively). No differences were found for T cytotoxic, PD1+ and NK-like T cells. The median amount of cEVs and PDL1+cEVs decreased from T0 to T1 (192000 vs 165000 /ul; 43100 vs 32000 /ul, respectively). In two patients achieving a TRG 0 and 1 an increased amount of cEVs and PDL1+cEVs was recorded. Overall, the amount of EVs expressing PDL1 on surface increased and the diameter of EVs enlarged (166 vs 175 nm). Conclusion: Our preliminary data showed that SCRT, in MSI-LARC patients, induced an immunologic polarization of TME. The altered expression of cells-PD1+ and cEVs-PDL1+ could enhance the activity of immune-check point inhibitors.Analysis is working in progress. References: ZhangW, TangY, Weil, et al. Preoperative short-course radiotherapy followed by chemotherapy and PD-1 inhibitor administration for locally advanced rectal cancer: A study protocol of a randomized phase II/III trial (STELLAR II study). Colorectal Dis , 2024 Sep;26(9):1732-1740 Laurenzana I, Lamorte D, Trino S, et al. Extracellular Vesicles: A New Prospective in Crosstalk between Microenvironment and Stem Cells in Hematological Malignancies. Stem Cells Int 2018,27:2018:9863194 Keywords: rectal cancer, TME, check-point inhibitor Poster Discussion 4870 High-fidelity Limited-Angle CBCT Imaging for Non- Coplanar Stereotactic Radiosurgery (SRS) / Stereotactic Body Radiation Therapy (SBRT) Siqi Ye, Xiaohan Xing, Yu Gao, Xuejun Gu, Hao Zhang, Lei Xing Radiation Oncology, Stanford University, Palo Alto, USA
Digital Poster 4864 Extracellular Vesicles and immune cells as
surrogates of tumor microenvironment changes in rectal cancer after short course RT. Preliminary data. Alessio Di Ciancia 1 , Fiorella D'Auria 2 , Daniela Lamorte 1 , Luciana De Luca 2 , Antonella Caivano 2 , Ilaria Laurenzana 2 , Luciana Valvano 3 , Teodora Statuto 3 , Ilaria Benevento 4 , Antonietta Montagna 4 , Barbara D'Andrea 4 , Luciana Rago 4 , Angela Pia Solazzo 4 , Antonella Bianculli 5 , Raffaele Tucciariello 5 , Alessio Vagliasindi 6 , Greta Di Stefano 6 , Carlo Calabrese 1 , Antonio Traficante 2 , Vito Metallo 4 , Grazia Lazzari 4 1 Laboratory of Preclinical and Translational Research, IRCCS CROB, Rionero in Vulture, Italy. 2 Clinical Pathology Unit, IRCCS CROB, Rionero in Vulture, Italy. 3 Laboratory of Clinical Research and Advanced Diagnostics, IRCCS CROB, Rionero in Vulture, Italy. 4 Radiation Oncology Unit, IRCCS CROB, Rionero in Vulture, Italy. 5 Physic Unit, IRCCS CROB, Rionero in Vulture, Italy. 6 Surgery Unit, IRCCS CROB, Rionero in Vulture, Italy Purpose/Objective: Ultra-hypofractionated RT may act as a catalyzer to enhance sensitivity to immunotherapy of tumor microenvironment (TME) in cold tumors like MSI- proficient locally advanced rectal cancer (MSI-LARC). Stellar II trial has demonstrated that, in MSI-LARC, the addition of the PD-1 inhibitor, sintilimab, significantly enhances the CR rate compared to Short Course RT (SCRT)-based TNT (1). To explain the immune additive effect of the SCRT, the peripheral immune cells (2) and circulating extracellular vescicles (cEVs) (3), as surrogates of TME polarization, were investigated in SCRT treated MSI-LARC patients. Chemotherapy was not allowed. Material/Methods: Eleven patients with MSI-LARC were treated with SCRT 5 Gy /25 Gy with VMAT on lower pelvis to include the T and N+ followed by surgery after 8-10 weeks. At baseline (T0) and one week off RT (T1), a sample of EDTA-peripheral blood and one of serum were collected for each patient. The percentage of B, T cells, T helper, T reg, T cytotoxic, T-double negative
Purpose/Objective: Efficient and high-fidelity image reconstruction under
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