Originated from CD44 expression data from de Jong et al. (45) in laryngeal cancer and confirmed in resected and chemo-radiotherapy treated HNSCC for CD44 and SLC3A2 (27, 46) in subsequent studies, it also became clear that tumor “stem cell-ness” is important in radiotherapy outcomes since these stem cell related biomarkers were associated with poor prognosis (35, 47–49). Here, CD44 is linked to head and neck squamous cell carcinoma.