ESTRO 2025 - Abstract Book

S1075

Clinical – Head & neck

ESTRO 2025

3260

Mini-Oral Subsite variation of HPV-related p16-expression in oropharynx cancer: Evaluation of frequency and prognostic impact in 8557 DAHANCA patients Pernille Lassen 1,2 , Jan Alsner 1 , Cathrine C Plaschke 3 , Christian Maare 2 , Hanne Primdahl 4 , Jørgen Johansen 5 , Maria Andersen 6 , Mohammad Farhadi 7 , Jens Overgaard 1 1 Department of experimental clinical oncology, Aarhus University Hospital, Aarhus, Denmark. 2 Department of oncology, Herlev Hospital, Copenhagen Univeristy, Herlev, Denmark. 3 ENT department, Rigshospitalet, Copenhagen University Hospital, Copenhagen, Denmark. 4 Department of oncology, Aarhus University Hospital, Aarhus, Denmark. 5 Department of oncology, Odense Univeristy Hospital, Odense, Denmark. 6 Department of oncology, Aalborg University Hospital, Aalborg, Denmark. 7 Department of oncology, Næstved Hospital, Næstved, Denmark Purpose/Objective: Separate staging criteria based on p16-expression is implemented in the TNM8 classification of oropharyngeal carcinoma (OPSCC). Recent data indicates significant oropharyngeal subsite differences in both the frequency of HPV-relation and the survival probability of the patients. Based on this complete, nationwide cohort study with prospectively collected data on consecutive patients collected over 35 years, we provide a detailed description of the subsite variation in OPSCC including an evaluation of the impact p16-expression on outcome. Material/Methods: For the present study, patients living in Denmark and referred for treatment of biopsy proven stage I-IV OPSCC diagnosed between 1986-2020 were identified in the DAHANCA database. HPV-association was determined by p16 status. Oropharyngeal subsite classification is registered in the DAHANCA database by the surgeon performing the diagnostic biopsy according to the TNM subsite classification. Tumors were subsequently grouped into “tonsil/base of tongue (BOT)”, “neighboring subsites” (tonsillar fossa & arch of the palate, glossotonsilar sulci and vallecula) and “distant subsites” (inferior surface of the soft palate, posterior wall and uvula). Results: A total of 8557 patients were identified with 5794 (68%) of tumors originating in “tonsil/BOT”, 1920 (22%) in “neighboring subsites” and 802 (10%) in “distant subsites”. Among tumors with known p16-status, a marked increase in the frequency of p16-positivity was seen in “tonsil/ BOT” tumors, from around 10-15% in the beginning of the study-period to reach approximately 75% in 2016-2020, Figure 1 . For tumors originating in “neighboring subsites” an increase in the proportion of p16-positivity was also evident but less pronounced (from 10-15% to 30 50%), whereas in “distant subsites” the percentage of p16-positive tumors remained low and stable over time (5 15%). Figure 2 demonstrates the 5-year risk of loco-regional failure according to subsite and p16-status in patients treated with curative intent (N=3327). The favorable prognostic impact of p16-positivity was confirmed only in “tonsil/BOT” and “neighboring subsites”, whereas tumors arising in “distant subsites” had a poorer outcome whether p16-positive or p16-negative.