Previously, studies have shown that CSCs from human primary HNSCC tissues or SCC cell lines have elevated aldehyde dehydrogenase (ALDH) activities.[14] Using an ALDEFLUOR kit, we sorted ALDHlow nonstem tumor cells and ALDHhigh CSC‐like cells with the specific ALDH inhibitor diethylaminobenzaldehyde (DEAB) as a control (Figure S3B, Supporting Information), and found that the circFAT1 expression was significantly higher in ALDHhigh CSCs than in ALDHlow tumor cells (Figure 3E). This evidence concerns the gene LDHA and head and neck squamous cell carcinoma.