“…Most studies (59%) were conducted in the USA, Canada, or European countries [34,35,37,39e41,43,45e48,50,52,54,57,59,60]. Twenty-one studies focused specifically on HNC patients [32,34e36, [32,40], larynx [42,51], nasopharynx [53,55,56], and oropharynx [45]. About 33% [36] up to 93% [51] of the study population consists of male HNC patients, while the gender proportion was unknown among eight studies [33,37,38,43,47,49,52,57].…”