p16 (CDKN2A, p16Ink4A), is key regulator of the cell cycle and involved in cell cycle control and cellular senescence. It is a specific inhibitor for Cdk4 and Cdk6 and binds to the phosphorylated Cdk-cyclin complex. A disruption of this pathway is commonly observed in cancer. p16 is lost in the majority of tumor cell lines and in most primary tumors. It is not expressed in melanoma. In carcinoma driven by an HPV (human papilloma virus) infection, p16 is often overexpressed. The antibody is especially useful for immunoprecipitation. The epitope was localized within the 15 aa residues of the C-terminus of p16 protein.