SOX2 and head and neck squamous cell carcinoma: We further examined whether SOX2 expression was associated with circFAT1 in human HNSCC by quantitative reverse transcriptase‐polymerase chain reaction (qRT‐PCR), and Pearson's rank correlation coefficient analysis also revealed a positive correlation between circFAT1 and SOX2 mRNA expression using 60 of frozen HNSCC tissue samples (Figure S3A, Supporting Information).