Abstract. Background: Human papillomavirus (HPV) is a favourable prognostic factor in oropharyngeal cancer. Moreover, we and others reported that HPV-positive cancer of unknown primary in the head and neck region (HNCUP) has better outcome than HPVHead and neck squamous cell carcinoma (HNSCC), including cancer of the pharynx, larynx, oral cavity, nose and nasal sinuses, often presents as a lump in the neck, and the specific site of the primary tumour is in general revealed after subsequent diagnostic procedures. However, in 2-9% of the cases the primary tumour is not found and the condition is denoted as cancer of unknown primary in the head and neck region (HNCUP) (1). Treatment of the latter has traditionally comprised of neck dissection followed by postoperative oncological treatment, i.e. radiotherapy, at times with the addition of platinum-based chemotherapy or cetuximab, while today in some cases only oncological treatment is given (2).Human papillomavirus (HPV)-associated oropharyngeal SCC is a HNSCC subset dominated by tonsillar and base of tongue SCC (3, 4). HPV-positive tonsillar and base of tongue SCC have increased in incidence in the past decades in the developed world and have better clinical outcomes than HNSCC in general [~80% vs. 40% 5-year overall survival (OS)] (5-8). HPV is frequently found in HNCUP and such cases likely have an HPV-positive oropharyngeal SCC origin, which gives reasons for steering diagnostic procedures as well as radiotherapy towards the oropharynx (9-11).Treatment de-escalation may be attainable in patients with HPV-positive HNCUP, similar to that discussed for patients with HPV-positive oropharyngeal SCC (12). Still, before HPV status of HNCUP can be used to guide treatment, more knowledge on the biology and clinical behaviour of the 665 Τhis article is freely accessible online.