Possible explanations for such heterogeneity in p16INK4A staining may include the inherent and unavoidable intra- and inter-observer variability in the morphological categorization of CIN, lack of standardization in the scoring of p16INK4A immunoexpression (nuclear and/or cytoplasmic staining; and positive vs. negative distribution within the epithelium), various antibody clones used for IHC and the existence of various HPV geographical variations (23). The gene discussed is CDKN2A; the disease is cervical squamous intraepithelial neoplasia.