ESTRO 2022 - Abstract Book

S374

Abstract book

ESTRO 2022

Theoretically a large tumour volume in patients treated with radiotherapy should confer a worse prognosis. However, recent studies in patients with p16-positive oropharyngeal squamous cell carcinoma (OPSCC) have provided inconsistent results. We investigated the role of primary tumour volume for patients with p16-positive and p16-negative OPSCC and in relationship to other prognostic factors. Materials and Methods We included 654 patients with OPSCC treated with primary radiotherapy (68.0 Gy to 73.1 Gy in 7 weeks, or 68.0 Gy in 4.5 weeks) within three prospective trials in the study. Local failure (LF), progression free survival (PFS) and overall survival (OS) in relationship to the size of the primary tumour volume and other established prognostic factors were investigated. Results The primary tumour volume and p16-status were found to be the strongest prognostic markers for LF, PFS and OS. For patients with p16-positive cancers the primary tumour volume was significantly more important compared with patients with p16-negative cancers. The importance of tumour volume was significant also within each T-classification. When adjusting for age, performance status, smoking status, sex, and hemoglobin-level the importance of tumour volume remained. The adjusted hazard ratio (HR) for OS per cm3 increase in tumour volume was 2.6 % (95% CI 0.2-4.9) for p16- positive and 1.3% (95% 0.3-2.2) for p16-negative.

Fig 1. Risk of local failure stratified by primary tumour volume in 654 patients with oropharyngeal cancer treated with radiotherapy.

Fig 2. Importance of primary tumour volume for local failure (dotted line), progression free survival (solid line) and overall survival (dashed line) within 3 years after radiotherapy. Blue bars (histogram) denote the number of patients in each volume-group (colour code as in Fig 1). Conclusion Outcome after radiotherapy for patients with OPSCC is largely determined by primary tumour volume, even when adjusting for other established prognostic factors. The primary tumour volume is significantly more influential for patients with p16- positive tumours.