ALDH1A1 and head and neck cancer: Previously, various CSC markers and self-renewal proteins such as CD133, CD44, ALDH1, ESA, β-Catenin, and SHH were found to be overexpressed in various cancers, including, but not limited to, pancreatic, head and neck cancer, prostate, breast, ovary, and lung cancer [3, 6, 35–39].