p16(INK4a) immunohistochemical overexpression is an overall reliable
surrogate marker of human papillomavirus (HPV)-associated
head and neck squamous cell carcinomas (
HNSCC). However, cases of ambiguous
p16(INK4a) overexpression are regularly detected in the head and neck:
p16(INK4a) expression can be observed in non-malignant tissue, such as tonsillar crypt epithelium and a proportion of
branchial cleft cysts. Additionally, diverse patterns of p16(INK4) expression can complicate interpretation of "
p16(INK4a) -positivity". These aspects impede the unrestricted application of
p16(INK4a) as a diagnostic marker in the head and neck. We hypothesized that combined detection of
p16(INK4a) and the proliferation marker Ki-67 could support clarification of ambiguous
p16(INK4a) expression in the head and neck by specifically indicating
p16(INK4a) -expressing cells with proliferative activity.
p16(INK4a) /Ki-67 co-expression in a combined staining procedure was correlated to distinct
p16(INK4a) expression patterns and HPV status (HPV
DNA followed by E6*I oncogene
mRNA detection) in 147
HNSCC and 50 non-malignant head and neck samples.
p16(INK4a) /Ki-67 co-expression only occurred in transformed cells of the head and neck. Co-expression was never detected in non-transformed cells. Combined
p16(INK4a) /Ki-67 expression was stringently associated with a diffuse
p16(INK4a) expression pattern. All HPV oncogene-expressing
HNSCC showed
p16(INK4a) /Ki-67 co-expression. We demonstrate that
p16(INK4a) /Ki-67 co-expression occurs exclusively in transformed cells of the head and neck. Our findings indicate a substantial impact of combined
p16(INK4a) /Ki-67 expression in the assessment of ambiguous
p16(INK4a) expression in the head and neck by specifically identifying
p16(INK4a) -expressing cells with proliferative activity. This property will be of considerable significance for head and neck histo- and cytopathology.