ESTRO 2025 - Abstract Book

S406

Clinical - Biomarkers

ESTRO 2025

Conclusion: Along with liver function, the NLR and PLR were prognostic factors in patients with liver metastases receiving SBRT treatment. Thus, the NLR and PLR could be prognostic biomarkers for liver mCRC primarily treated with SBRT.

Keywords: Liver metastases, SBTR, Biomarkers

60

Digital Poster Circulating tumor DNA as a comprehensive recurrence risk biomarker after ablative radiotherapy for early stage non-small cell lung cancer Masaki Nakamura 1 , Shun-Ichiro Kageyama 1 , Hidenari Hirata 1 , Masaki Ohira 2 , Yumi Hakozaki 1 , Hidehiro Hojo 1 , Takeshi Fujisawa 1 , Riu Yamashita 2 , Hiroshi Haeno 3 , Akinori Kanai 4 , Yutaka Suzuki 4 , Katsuya Tsuchihara 2 , Sadamoto Zenda 1 1 Radiation Oncology, National Cancer Center Hospital East, Chiba, Japan. 2 Translational Informatics, Exploratory Oncology Research and Clinical Trial Center, National Cancer Center, Chiba, Japan. 3 Research Institute for Biomedical Sciences, Tokyo University of Science, Chiba, Japan. 4 Computational Biology and Medical Sciences, Graduate School of Frontier Sciences, University of Tokyo, Chiba, Japan Purpose/Objective: We reported that detectable pretreatment circulating tumor DNA (ctDNA) was associated with inferior progression free survival (PFS) for early-stage lung adenocarcinoma patients treated with ablative radiotherapy [1]. In this study, we evaluated the applicability of our ctDNA detection method in non-small cell lung cancer (NSCLC) by adding the results from squamous cell carcinoma and pathologically unproven patients to those from adenocarcinoma. Material/Methods: Patients diagnosed with cT1-2N0M0 non-small cell lung cancer (NSCLC) and treated with proton beam therapy at our institution from January 2014 and December 2019 were selected. Patients without pathologically unproven were also included. Pretreatment plasma and matched white blood cell samples were subjected to targeted sequencing. The cumulative incidence curves of recurrence were calculated and compared using Gray's test. PFS and overall survival (OS) curves were constructed using the Kaplan-Meier method and were compared using the log rank test and Cox proportional hazards model. Results: Of the 62 patients who met sequence quality, ctDNA was detected in 14 patients. By histological type, 19% (8/43) were detected in adenocarcinoma, 40% (4/10) in squamous cell carcinoma, and 22% (2/9) in pathologically unproven. The median follow-up period was 61 months (95%CI: 58-67 months), calculated using the reverse Kaplan–Meier method. In squamous cohort, detectable ctDNA was significantly associated with poor PFS (P=0.01) and tended to be associated with poor OS (P=0.08). In pathologically unproven cohort, detectable ctDNA was associated with inferior PFS (P =0.02,) and OS (P<0.01). When three cohorts were integrated, detectable ctDNA was significantly associated with inferior PFS (hazard ratio [HR] 4.4; 95% CI 2.0-9.6; P <0.01) and OS (HR, 4.2; 95% CI, 1.4 12.2; P<0.01). Regarding the recurrence site, there was no significant difference in the rate of in-field failure according to ctDNA detection (3-year cumulative incidence: 21.4% vs. 10.5%, P=0.26), but the ctDNA-positive group showed a significantly higher rate of out-of-field failure (3-year cumulative incidence: 57.1% vs. 25.3%, P =0.01) than the ctDNA-negative group. Conclusion: Our ctDNA detection method was applicable to squamous cell carcinoma and to pathologically unproven. These results suggest that pretreatment ctDNA analysis can be a comprehensive biomarker that can predict recurrence in