Introduction
While lung cancer is the leading cause of cancer‑related mortality and is predominantly caused by tobacco smoke, ~25% of all lung cancers worldwide are not attributable to tobacco smoke (1). In fact, in a large Japanese cohort study of >20,000 patients with non‑small cell lung cancer (NSCLC), 30% were never‑smokers (2). Lung cancer in never‑smokers is unique with regard to its clinical characteristics and is suggested to be a distinct disease, which has emerged as a global public health concern (3,4). Investigations into the molecular mechanisms responsible for the disease are urgently necessary in order to improve therapeutic strategies. A number of etiological factors have been proposed, with infection with oncogenic human papillomavirus (HPV) as one of these (5‑7). A recent study on the comprehensive genome sequencing of cancer revealed that the apobec3b protein was associated with carcinogenesis in multiple cancers, including lung cancer (8). Viral infection is known to play a significant role in upregulating proteins. In fact, cervical cancer and pharyngo‑laryngeal cancer have been classified into a unique mutational signature that is associated with HPV (8).a