ESTRO 2025 - Abstract Book

S3987

Radiobiology - Tumour radiobiology

ESTRO 2025

2001

Poster Discussion Ex vivo irradiation of oropharyngeal carcinoma biopsies to predict tumor radiation response: results of the first 100 patients. Gerda M. Verduijn 1 , Iris Lauwers 1 , Katrin Pachler 2 , Nicole S. Verkaik 2 , Aniel Sewnaik 3 , Stijn Keereweer 3 , Jose Hardillo 3 , Dominiek Monserez 3 , Bernd Kremer 3 , Hetty Mast 4 , Brend P. Jonker 4 , Sjors Koppes 5 , Bianca Mostert 6 , Mischa S. Hoogeman 1 , Steven F. Petit 1 , Dik C. van Gent 2 , Marta Capala 1 1 Radiotherapy, Erasmus MC Cancer Institute, Rotterdam, Netherlands. 2 Molecular Genetics, Erasmus MC Cancer Institute, Rotterdam, Netherlands. 3 Otorhinolaryngology and Head and Neck surgery, Erasmus MC Cancer Institute, Rotterdam, Netherlands. 4 Oral and Maxillofacial surgery, Erasmus MC Cancer Institute, Rotterdam, Netherlands. 5 Pathology, Erasmus MC Cancer Institute, Rotterdam, Netherlands. 6 Medical Oncology, Erasmus MC Cancer Institute, Rotterdam, Netherlands Purpose/Objective: The largest bottleneck for effective personalization for oropharyngeal squamous cell carcinoma (OPSCC) is our inability to predict the response of individual patients to (chemo-)radiation (1). Recent research has shown that tumor tissue can be kept viable ex vivo for more than five days (2,3). This enables, in theory, to take a biopsy of the patient, treat the tissue, and study the tissue response ex vivo , to capture biological differences between tumors to predict patient response, before the start of treatment. The goal of the current study was to investigate the feasibility of this functional test during the diagnostic work-up. Material/Methods: For the test to have potential in a routine clinical setting, the following is required: (i) it should be tolerable for patients, (ii) biopsy tissue should remain viable ex vivo for five days, (iii) and should contain sufficient tumor cells, (iv) and the response ex vivo should be representative for the clinical response. All patients with OPSCC scheduled for curative (chemo-)radiation between August 2020 and December 2022 were offered participation in our clinical study. Tumor biopsies were obtained at the outpatient clinic by the transoral or fiberoptic approach, or under general anaesthesia, and cut into 300 µm slices. Tumor slices were untreated, or irradiated with a single dose of 5Gy X-rays. Radiation response after five days of culture was assessed using EdU incorporation, visualizing proliferating cells. Samples were defined as sensitive (> 66% decrease in proliferation relative to control), intermediate (33-66% decrease), or resistant to radiation (<33% decrease) (2). Results: In total 150 patients met the eligibility criteria. Of those, 100 (66.7%) patients were included (req (i)). Fifty-six percent of biopsies were viable after five days of culture (req (i)). The number of viable biopsies was higher (64%) in the second 50 compared to the first 50 patients (48%). Fifty-seven percent of viable biopsies were suitable for analysis (req (iii)). Marked differences in ex vivo radiosensitivity groups was observed in line of what could be expected clinically between the following patient categories (req (iv)): HPV + and never smokers, HPV + and former/ current smokers, and HPV - (Figure).