Immunohistochemical analysis of CHRNA5, CES1, Pan-ck, PCNA, Ki-67, and E-cadherin in tumor tissues and human laryngeal and hypopharyngeal cancer specimens showed that CHRNA5 regulates CES1 expression via the MEK/ERK pathway, affecting the recurrence and metastasis of head and neck squamous carcinoma (Fig. 12). This evidence concerns the gene PCNA and hypopharynx cancer.