KEY POINTS
- This multicentre retrospective study included 271 patients with non-metastatic oropharyngeal squamous cell carcinoma treated with definitive intensity-modulated radiotherapy at four institutions between 2008 and 2022; 84.9% were human papillomavirus-positive and 93.7% received concurrent systemic therapy.
- Gross tumour volume was measured on pretreatment and adaptive replanning computed tomography after 14–16 fractions. Tumour volume reduction above 40% was used to classify response.
- At a median follow-up of 53 months, five-year overall survival was 90.9% versus 77.9% for tumour volume reduction above versus at or below 40% (p = 0.003); five-year progression-free survival was 79.0% versus 68.5%(p = 0.039).
- Tumour volume reduction above 40% remained independently associated with improved overall survival (hazard ratio 0.432, 95% confidence interval 0.221–0.846; p = 0.014) and cancer-specific survival (hazard ratio 0.292, 95% confidence interval 0.113–0.757; p = 0.011), but not progression-free survival after multivariable adjustment.
- Late treatment-related toxicity occurred in 8.1% of patients, most commonly mucosal necrosis in 5.5%; toxicity was not significantly associated with tumour volume reduction.
CLINICAL TAKEAWAY
Tumour shrinkage measured on routine adaptive replanning imaging may add dynamic prognostic information beyond baseline stage and human papillomavirus status, particularly for overall survival. However, the retrospective design, centre imbalance, contouring variability and internally derived 40% threshold mean the finding should not yet guide treatment de-intensification or escalation outside prospective studies.