Tumor volume as a prognostic marker in p16-positive and p16-negative oropharyngeal cancer patients treated with definitive intensity-modulated radiotherapy.

PURPOSE

To investigate the impact of primary gross tumor volume (pGTV) and nodal gross tumor volume (nGTV) in oropharyngeal squamous cell carcinoma (OPSCC) and the difference in their role between human papillomavirus (HPV)-positive and HPV-negative patients.

METHODS

The patient cohort consists of 91 OPSCC patients treated with definitive radiochemotherapy or radiotherapy using intensity-modulated radiotherapy (IMRT). All patients had a minimum follow-up of 31 months. Volume measurements were made from computer tomography (CT) scans and HPV status was assessed by p16 immunohistochemistry. The end points were as follows: overall survival (OS), disease-free survival (DFS) and locoregional control (LRC).

RESULTS

pGTV was a significant independent prognostic factor for overall survival (OS; p = 0.020) in p16-negative patients. nGTV of p16-negative tumors had significant prognostic value in all end points in multivariate analyses. High-stage (III-IVc) p16-negative tumors were only associated with significantly poorer OS (p = 0.046) but not with poorer LRC or DFS when compared with the low-stage (I-II) tumors. nGTV of p16-positive tumors was an independent prognostic factor for DFS (p = 0.005) and LRC (p = 0.007) in multivariate analyses.

CONCLUSION

pGTV may serve as an independent prognostic factor in p16-negative patients and nGTV may serve as an independent prognostic factor both in p16-positive and p16-negative patients treated with radiochemotherapy or radiotherapy using IMRT. Tumor volume may have an impact on selecting patients for de-escalation protocols in the future, both in p16-positive and p16-negative patients.