High-dose loco-regional pattern of failure after primary radiotherapy in p16 positive and negative head and neck squamous cell carcinoma – A DAHANCA 19 study

Introduction Patients with failure after primary radiotherapy (RT) for head and neck squamous cell carcinoma (HNSCC) have a poor prognosis. This study investigates pattern of failure after primary curatively intended IMRT in a randomized controlled trial in relation to HPV/p16 status. Material and methods Patients with HNSCC of the oral cavity, oropharynx (OPSCC), hypopharynx or larynx were treated with primary curative IMRT (±cisplatin) and concomitant nimorazole between 2007 and 12. Of 608 patients, 151 had loco-regional failure within five years, from whom 130 pairs of scans (planning-CT and diagnostic failure scan) were collected and deformably co-registered. Point of origin-based pattern of failure analysis was conducted, including distance to CTV1 and GTV, and estimated dose coverage of the point of origin. Results Of 130 patients with pairs of scans, 104 (80 %) had at least one local or regional failure site covered by 95 % of prescribed dose and 87 (67 %) of the failures had point of origin within the high-dose CTV (CTV1). Of failures from primary p16 + OPSCC, the majority of both mucosal (84 %) and nodal (61 %) failures were covered by curative doses. For p16− tumors (oral cavity, OPSCC p16neg, hypopharynx and larynx), 75 % of mucosal and 66 % of nodal failures were high-dose failures. Conclusion Radioresistance is the primary cause of failure after RT for HNSCC irrespective of HPV/p16 status. Thus, focus on predictors for the response to RT is warranted to identify patients with higher risk of high-dose failure that might benefit from intensified treatment regimens.