CD44 and head and neck cancer: It should be noted that, alongside tissue biomarkers, the study of saliva biomarkers, including the soluble form of CD44, has become a promising diagnostic tool in various general diseases [31], non-oral tumors [32], and oral diseases (especially chronic periodontitis and lichen planus) [22,33,34,35], as well as helpings in early (stage I and II) detection of oral squamous cell carcinoma, oropharyngeal cancers [36], and other head and neck cancers [36,37,38,39,40].