ESTRO 2025 - Abstract Book

S1079

Clinical – Head & neck

ESTRO 2025

Gentofte,, Herlev, Denmark. 9 Department of Experimental Clinical Oncology, Aarhus University Hospital, Aarhus, Denmark. 10 Department of Otorhinolaryngology Head and Neck Surgery and Audiology, Copenhagen University Hospital Rigshospitalet, Copenhagen, Denmark Purpose/Objective: Nasopharyngeal carcinoma (NPC) is a rare malignancy in most populations, but is endemic in specific regions, including parts of Asia, North Africa, and the Arctic. In these endemic regions, NPC is ubiquitously associated with Epstein-Barr virus (EBV), whereas both EBV-positive and EBV-negative tumors are observed in non-endemic areas. NPC is a challenging disease to treat, and radiotherapy remains the corner stone in the treatment with or without chemotherapy. While most studies on NPC failure patterns focus on endemic regions, data on failures in low incidence populations are limited. Therefore, to supplement earlier data on the epidemiology(1), we conducted an analysis of failure patterns in all NPC patients treated with definitive radiotherapy in Denmark 2000-2018. Material/Methods: Patients with NPC treated with definitive radiotherapy in Denmark from 2000 to 2018 were identified through the Danish Head and Neck Cancer Study Group (DAHANCA) Database (n=331). Medical records were reviewed to supplement missing data and to determine tumor EBV status. Follow-up continued until December 31, 2023, with treatment failure classified as locoregional (T, N, TN) or distant (M, TM, NM, TNM). The cumulative incidence of locoregional failure (LRF) and distant failure (DF) was evaluated in competing risk analysis with death considered a competing event. The influence of predefined variables on LRF and DF was assessed in multivariate Cox regression analysis. Results: Most patients presented with locally advanced disease (see Table 1). At the end of follow up treatment failure had occurred in 119 of 331 (36%) patients, distributed as 70/119 (59%) LRF and 49/119 (41%) DF. The five-year cumulative incidence rates for LRF and DF were 17% and 14%. In multivariate analysis DF but not LRF was significantly associated with locally-advanced disease: Stage III (HR=7.38, 2.54-21.46), stage IVa (HR=7.14, 2.43;20.95). The five-year cumulative incidences of DF by stage were: I=0%, II=4%, III=19% and IVa=21% (see Figure 1). The five year overall failure rates with competing risk analysis were 32% (24-41%) in 2000-2007 and 30% (24-37%) in 2008 2018. EBV-status was determined in 198/331 tumors, with 145 (73%) positive. Overall failure rates were similar in EBV positive (30%) and negative (32%). The five-year OS for the cohort was 63.1% (60-68%). EBV-positive patients had significant higher five-year OS (79.3%) compared to EBV-negative (58.5%) and EBV-unknown (47.4%) (p<0.01). Conclusion: NPC failure rates showed no temporal change, with distant metastasis risk remaining high in advanced-stage disease. The failure rates were similar in EBV-positive and EBV-negative NPC, but survival was superior in EBV positive NPC.