ESTRO 2024 - Abstract Book

S1407

Clinical - Head & neck

ESTRO 2024

Although recent phase III trial data show high cure rates for human papilloma virus (HPV)-driven squamous cell carcinoma of the oropharynx (OPSCC) (1), outcomes are heterogeneous depending on risk stratification (2), and prognosis for patients failing primary radical therapy is poor (3). Conversely, and despite contemporary IG-IMRT techniques, radical chemo-radiation remains highly toxic, with significant long-term morbidity (4). Therefore, biomarker driven personalisation of treatment and follow-up protocols is an important area of investigation for OPSCC. Quantification of HPV cell-free DNA (cfDNA) in the plasma of patients with HPV related OPSCC is a non-invasive and inexpensive technique, and a promising development to address this unmet need (5). However, the relationship between assays measuring HPV cfDNA, and disease burden remain poorly understood. The purpose of this study was to assess whether baseline measurement of plasma HPV correlates with disease volume in patients undergoing radical radiation-based treatment for OPSCC SR1171 is a prospective, single centre study in which HPV cfDNA is collected from patients with non-metastatic OPSCC undergoing treatment with curative intent pre-treatment, and 3 monthly for 3 years post completion of radical therapy. 174 patients were recruited from November 2018 to September 2022. For this sub-study, the first 100 recruited patients with p16+ve disease based on tumour histopathology were assessed. ddPCR assays of plasma cfDNA were carried out to detect the following HPV genotypes – 16, 18, 31, 33 & 35 - as described in previously published work (6). Baseline HPV cfDNA results were compared with segmented tumour volumes on radiotherapy planning CT scans. All segmentations were undertaken by 2 experienced consultant oncologists, both with >10 years’ experience managing OPSCC. Primary (GTVp), and nodal (GTVn) tumour volumes were segmented and recorded separately and summed to total GTV (GTVt). Segmentations were undertaken in Varian Eclipse v13.6, according to contemporary clinical trial protocols (4,6). Segmentations were conducted entirely blind to knowledge of baseline HPV cfDNA copy number. Statistical analysis was done in R v4.3.0. Absolute baseline HPV cfDNA copy-numbers were transformed to log2, and scatter plots used to visualise relationship with tumour volumes (GTVp, GTVn, and GTVt). Tumour volume variables were not normally distributed, therefore Spearmans ρ statistics were calculated for each tumour volume. Material/Methods:

Results:

Patients were excluded from analysis for the following reasons: failed (0 copy number) assay result – 9, primary surgical management (TORS +/- neck dissection) – 7, induction chemotherapy – 8, leaving 76 patients for analysis. Baseline data for these patients are presented in Table 1.

Number

%

Gender

Male

55

72.4

Female

21

27.6

T-stage