ALDH1A1 and head and neck squamous cell carcinoma: Bourguignon et al., have widely demonstrated that a high level of CD44 with ALDH1 detected in the subpopulation of human HNSCC-CSC display the hallmark of stem cell properties, including NANOG, OCT4, and SOX2 expression, self-renewal capability and high tumorigenic potential in immunosuppressed mice44.