ESTRO 2025 - Abstract Book

S1001

Clinical – Head & neck

ESTRO 2025

1897

Proffered Paper Treatment Response-Adapted Risk Index Model for Survival Prediction and Adjuvant Chemotherapy Selection in Nonmetastatic Nasopharyngeal Carcinoma Liu Yang, Yi Junlin Department of Radiation Oncology, National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China Purpose/Objective: Dynamic response to therapy is strongly associated with cancer outcomes. We aim to develop and validate the model response-adapted individualized risk index (RAIRI) as an individual prognostic approach and predictive biomarker for adjuvant chemotherapy (AC) benefit in nonmetastatic nasopharyngeal carcinoma (NPC) based on pretreatment clinical characteristics, longitudinal plasma cell-free Epstein–Barr virus DNA (cfEBV-DNA), and tumor regression measurements collected during treatment. Material/Methods: RAIRI was tested in 2,148 patients across training, internal validation, external validation, and randomized controlled trial (RCT) cohorts from three academic cancer centers. Bayesian joint model was employed for integrative prediction. Prognostic accuracy was evaluated using calibration, concordance indices (C-indices), and areas under the curves (AUCs). RAIRI’s performances of predicting AC benefit were examined in patients from two RCTs (NCT02958111 and NCT02143388) designed to assess AC’s benefit in high-risk stage III/IVA NPC. Results: RAIRI incorporates six pretreatment characteristics (age, T-stage, N-stage, cfEBV-DNA, lactate dehydrogenase, and central-nodal-necrosis), longitudinal cfEBV-DNA, and tumor regression measurements (Figure 1). RAIRI predictions were made in the context of time and refined using serially collected longitudinal data (Figure 2). In the training cohort, RAIRI demonstrated accurate calibration and high prognostic accuracy (C-index 0.849, AUC 0.895), significantly superior to the conventional models. The internal validation, external validation, and RCT cohorts confirmed RAIRI’s prognostic accuracy with C-indices and AUCs all over 0.8. In the RCT cohort, RAIRI identified approximately 70% of low-risk patients that did not benefit from AC, whereas the high-risks experiencing substantial benefits from AC versus observation (5-year PFS, 58.7% vs. 22.8%; HR=0.40; 95% CI, 0.22–0.73). Predictive performance of RAIRI for AC benefit was consistent across various clinical subsets and beyond post radiotherapy cfEBV-DNA.