ESTRO 2025 - Abstract Book

S1868

Clinical – Upper GI

ESTRO 2025

Results: The relative CD8+ and CD4+ T cell fractions increased at the end of treatment up to FU2, indicating an anti-tumoral T cell response. despite a significant drop in the absolute cell counts. The analysis confirmed the increased fraction of proliferating CD8+ and CD4+ T cells, including PD-1+ and PD-1– CD8+ and CD4+ T cells. The T cells showed increased levels of exhaustion markers (PD-1, Tim-3, CTLA-4), and most T cells expressed PD-1. Tumor-reactive T cells have been found among PD-1 expressing T cellsAt the end of treatment there was a significant increase in activated non-exhausted PD-1+Tim-3– CD8+ and CD4+ T cells, which lasted until the FU2 for CD4+ T cells. Expression of the activation marker ICOS was accordingly increased at the end of treatment up to the FU2 for CD4+ T cells. There was a significant drop of CD8+ and CD4+ T-cells expressing the chemokine receptor CXCR3, important for T cell trafficking, which was more pronounced in CD4+ T cells. Expression of IFNg was increased in CD8+ and CD4+ T cells at the end of treatment up to the FU2. TNF-a expression in CD8+ T cells was strongly increased at the end of treatment up to FU2, and GrzB expression increased in CD8+ and CD4+ T cells at FU1. The relative and absolute numbers of NK and NKT cells were strongly reduced mainly at the end of treatment up to the FU2. There was also a significant increase in immunosuppressive Treg and MDSC. Conclusion: SBRT induced lymphopenia, but also lymphocyte activation and proliferation in liver cancer patients. Although T cells and NK cells showed good functionality, as indicated by the strong expression of IFN-g and TNF-α. Future studies should examine the relative impact of these changes on patient outcome and scheduling of immunotherapy.

Keywords: Liver, HCC, SBRT, Immune modulation

4436

Digital Poster Single centre experience with Stereotactic Ablative Body Radiotherapy for liver oligometastases Carmen Cañadillas Navero 1 , Iñigo San Miguel Arregui 1 , Celia Nicolás Boluda 1 , Gemma Alberca Hernández 1 , Belen Cuesta Picón 1 , Sara Medina López 1 , Jorge Ruiz Martínez de Azagra 1 , Sofía García Repiso 2 1 Radiation Oncology, Salamanca University Hospital, ISBAL, Salamanca, Spain. 2 Radiophysics, Salamanca University Hospital, ISBAL, Salamanca, Spain

Purpose/Objective: To evaluate clinical outcomes and predictive factors for local control in patients with liver oligometastasis.

Material/Methods: A retrospective analysis was conducted including demographics and baseline metastases characteristics of 49 patients. Inclusion criteria were ECOG performance status of 0 or 1, no brain metastases, and lesions < 5.5 cm. The main variables measured were local control, overall survival, and toxicity. Follow-up imaging, including PET-CT, CT scan, or MRI, was used for evaluation, and toxicity was assessed according to CTCAE v5.0 criteria. Results: The cohort included 49 patients with 74 metastases. The median age at diagnosis was 66 years. Primary tumors’ most frequent histology was adenocarcinoma (76,6%) and the most common origin was colorectal (66,2%). Metastatic stage at diagnosis (Stage IV) was found in 44% of the patients. Of the entire cohort, 80% of the patients had a prior history of metastasis. The total number of metastases throughout clinical history observed in the cohort was 1 (20,8%), 2 (22,1%), 3 (16,9%) and ˃ 3 (40,2%). 67,35% had received previous treatment before SABR. Of these, 27 presented with oligoprogression. Radiotherapy planning CT scans were performed with active breathing control for 41.6% of patients. 4D-CT imaging was used to assess tumor motion for the 42.9% unable to tolerate breath hold. Seven patients (9%) were scanned using abdominal compression and 5 (6,5%) PET-CT scan. Fiducial markers were