CD44 and head and neck squamous cell carcinoma: In addition, BMI1 is highly expressed in cisplatin-resistant and metastatic HNSCC cells, which exhibit CSC characteristics along with enhanced AP-1 activity and IL-6 signaling as well as the expression of stemness markers, such as aldehyde dehydrogenase (ALDH) and CD44 [89,90,97,98,99,100].