To explore the relationship between CircRNA_ACAP2 and miR-21-5p in various HNSCC cells, we examined the expression levels of CircRNA-ACAP2 (Figure 4C) and miR-21-5p (Figure 4D) in different HNSCC cell lines, namely, HN-4, HN-9, HN-30, SCC-4, SCC-9, SCC-25, and CAL-27. Here, ACAP2 is linked to head and neck squamous cell carcinoma.