CD44 and head and neck squamous cell carcinoma: Besides CD44 and ALDH1, several other stem cell markers have been described for HNSCC, such as Bmi-1, CD133, Nanog, Oct-4, and SOX2 (Satpute et al., 2013; Patel et al., 2014; Qian et al., 2015) and those have partly been associated with prognosis (Chen et al., 2014; Dong et al., 2014; Zhou and Sun, 2014).