PKM and head and neck squamous cell carcinoma: It is important to note that SFRP4, a driver gene, upregulated in HNSCC, is regulated by five different circRNAs, namely, hsa_circ_0008309| CUL3, hsa_circ_0001387| WHSC1, hsa_circ_0036186| PKM2, hsa_circ_0002667| MGAT2, and hsa_circ_0001821| circPVT1, in the identified triad.