<qa>  What is the main cause of HNCs recurrence?Head and neck cancer HNC is the sixth leading incident cancer worldwide with 600,000 cases expected in 2012.1 The vast majority of cases are head and neck squamous cell carcinoma HNSCC, comprising 90 of histologies. Despite advances in multimodality therapy for HNSCC, 5-year overall survival OS is 40-60, and has increased only incrementally in the past two decades.2 Improved prognosis is largely attributable to the emerging epidemic of oral human papillomavirus infection HPV. An increasing proportion of oropharyngeal HNC is driven by oncogenic HPV, rather than the classic risk factors of tobacco and alcohol; HPV etiology is associated with improved survival after conventional treatments.3,4 Most patients with HNC present with locally advanced disease stage III-IVb, and have associated anatomic deformity due to the primary tumor or neck adenopathy. Intensive multi-modality therapy including surgery, chemotherapy, and radiotherapy is routinely required. The current standard of care for primary nonsurgical management of previously untreated locally advanced PULA HNSCC is concurrent cisplatin-radiotherapy RT, as administered in the sentinel Intergroup trial 0126 5,6. Likewise, the standard of care in the adjuvant management of high risk disease is cisplatin-RT as proven in the Radiation Therapy Oncology Group RTOG 95-01 and European Organization for Research and Treatment of Cancer EORTC 22931 trials.7,8 Despite curative-intent surgical or non-surgical therapy, approximately half of people will relapse. Unlike most other epithelial malignancies, the dominant pattern of relapse and the driver of HNC-related mortality is locoregional recurrence.9 The vast majority of recurrences occur within the first two years following definitive therapy. 