ALDH1A1 and head and neck squamous cell carcinoma: There is a significant overlap in the ALDH and CD44 populations with 50.6%–74.4% of ALDH1+ cells expressing CD44 and only 9.8%–23.6% of CD44 cells demonstrating high ALDH activity indicating that ALDH1 may be a more specific marker of CSCs in HNSCC [80].