CDKN2A and neoplasm: However, it is of particular note that, in our study, the Ki-67 proliferation index in areas with diffuse nuclear or cytoplasmic p16INK4a staining in at least 20% of tumor cell areas, or even in over 50% of tumor cell areas, was significantly higher in HPV-positive tumors than in the corresponding p16INK4a stained areas of HPV-negative tumors (p = 0.003 and p = 0.004, respectively).