LGR5 and oral cavity squamous cell carcinoma: GPR49, also known as Lgr5, that plays a critical role in various cancers, including basal cell carcinoma, head and neck squamous cell carcinoma, oral squamous cell carcinoma, and hepatocellular carcinoma (Yamamoto et al., 2003; Tanese et al., 2008; Major et al., 2013).