S671
Clinical – Head & neck
ESTRO 2026
treatment strategies and follow-up intensity. Material/Methods:
platinum-based chemotherapy (3 cycles on average), followed by locoregional radiotherapy (70 Gy in 33-35 fractions), mainly with IMRT (76%). Concomitant chemotherapy was associated in 98% of cases. These treatments were associated with adverse effects, including radiodermatitis (100%) and mucositis (98%, including 18% grade 3). Twenty-four percent of patients received maintenance chemotherapy with capecitabine, and 44% received local treatment of metastases. At 3 years, progression-free survival (PFS) was 18% and overall survival (OS) was 44%. Univariate analysis showed a significant impact of several factors on PFS (gender, T stage, interruption of radiotherapy, maintenance chemotherapy). Multivariate analysis did not identify any independent prognostic factor for PFS. However, for OS, T stage (p = 0.024) and metastatic site (p = 0.001) emerged as independent prognostic factors. Conclusion: Advanced stages (T3-T4) and bone metastases are poor prognostic factors that significantly impact overall patient survival. Our study aimed to evaluate radiotherapy practices in Salah Azaiez’s Institut; however, a larger-scale study would be even more beneficial. Keywords: radiotherapy, oligometastatic, nasopharyx Digital Poster 5012 Biological Half-Life of cfHPV DNA as a Marker of Surgical and Radiotherapeutic Response Radka Lohynska 1,2 , Michal Lacek 1,2 , Ale š Č o č ek 3 , Zuzana Krátká 3 , Zuzana Vojt ě chová 4 , Martina Saláková 4 , Jana Š mahelová 4 , Ruth Tachezy 4 1 Department of Oncology, Thomayer University Hospital, Prague, Czech Republic. 2 First Faculty of Medicine, Charles University, Prague, Czech Republic. 3 Department of Otorhinolaryngology and Head and Neck Surgery, Thomayer University Hospital, Prague, Czech Republic. 4 Department of Genetics and Microbiology, Faculty of Science, Biocev, Charles University, Prague, Czech Republic
Pilot study included 26 patients with HPV-positive oropharyngeal squamous cell carcinoma (OPSCC) treated between 2023 and 2024. Of these, 15 patients underwent surgical resection with neck dissection ± postoperative radiotherapy, while 11 received definitive radical radiotherapy. Tumour staging was performed according to the 8th edition of the TNM classification. Circulating cell-free HPV DNA (cfHPV DNA) was quantified using digital droplet polymerase chain reaction (ddPCR), and cfHPV DNA elimination half-times were subsequently calculated. Results: A radical R0 resection was achieved in 9 patients, R1 resection in 5 patients, and R2 resection in 1 patient, while 11 patients underwent definitive radiotherapy or chemoradiotherapy. The corresponding cfHPV DNA elimination half-times were 2.9, 6.5, 53.8, and 106.7 hours, respectively (p < 0.001). These results demonstrate that cfHPV DNA kinetics significantly differ across treatment modalities and suggest that, in surgically treated patients, cfHPV DNA clearance may serve as an early biomarker for postoperative risk stratification. Conclusion: cfHPV DNA elimination kinetics vary significantly across treatment modalities in HPV-positive oropharyngeal cancer. The markedly shorter cfHPV DNA half-life following radical surgical resection compared with incomplete resections or radiotherapy suggests a close relationship to residual tumour burden. In surgically treated patients, rapid cfHPV DNA clearance may therefore serve as a valuable early biomarker for postoperative risk stratification and tailoring of adjuvant therapy. References: Hollander A, Nonaka T. Cell-free HPV-DNA as a high- accuracy biomarker for treatment de-escalation in HPV-positive head and neck squamous cell carcinoma. Front Oncol. 2025 Sep 18;15:1569877. doi: 10.3389/fonc.2025.1569877.Stawarz K, Gorzelnik A, Klos W, et al. Clinical Utility and Limitations of Circulating HPV DNA in Tonsillar Squamous Cell Carcinoma: A Narrative Review. Cancer Control. 2025 Jan-Dec;32:10732748251372683. doi: 10.1177/10732748251372683.Supported by grants from the Ministry of Health of the Czech Republic - RVO (Thomayer University Hospital - FTN, 00064190) and The National Institute for Cancer Research Project (Programme EXCELES, ID Project No. LX22NPO5102) - Funded by the European Union - Next Generation EU. Keywords: cfHPV DNA
Purpose/Objective: Circulating cell-free HPV DNA (cfHPV DNA) is
detectable in the plasma of patients with HPV-driven oropharyngeal squamous cell carcinoma (OPSCC) and represents a promising biomarker for treatment monitoring and minimal residual disease detection. Quantitative fluctuations in cfHPV DNA levels immediately following surgical resection or during radiotherapy (RT) closely correlate with therapeutic response and recurrence risk. Short biological half-life of cfHPV DNA allows early evaluation of residual tumour burden or micrometastatic persistence, offering valuable guidance for tailoring adjuvant
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