Test Details: Immunohistochemical testing helps to identify specific antigens (proteins) within tissue sections utilizing an antigen-specific antibody. P16 (also known as INK4a or cyclin-dependent kinase inhibitor 2A) is a tumour suppressor protein encoded by the p16INK4a gene. p16 is overexpressed in HPV-associated intraepithelial dysplasia and squamous cell carcinomas of different origins including vulvar, vaginal, and cervical squamous cell carcinoma in addition to oropharynx carcinoma. In routine immunohistochemistry, p16 reveals cytoplasmic and nuclear staining pattern and the intensity of the stain correlates with grade of HPV infection and grade of associated dysplasia. p16 is also highly expressed in uterine serous carcinoma and a helpful marker that labels the cells of serous tubal intraepithelial carcinoma (STIC).