p16INK4a is a cyclin-dependent kinase (CDK) inhibitor, and binds CDK4 and CDK6 and inhibits their kinase activity. It is also called MTS1 and INK4a, and p15INK4b (MTS2), p18INK4c and p19INK4d are other members of the INK4 family. p16INK4a is a tumor suppressor gene, and inactivation is seen in many cancer tissues and cancer cell lines as a result of mutations or hypermethylation. However, overexpression of p16INK4a has been reported in several tumors, including cervical cancer. Infection with human papilloma virus (HPV) plays a large role in the cases of cervical cancer. Assessment of overexpression of p16INK4a by immunohistochemistry methods has been shown to be more useful in research of cervical dysplasia than existing methods of detection of high-risk-group HPV infection.