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  1. Stefano Serra,
  2. Runjan Chetty
  1. Department of Anatomical Pathology, Laboratory Medicine Program, University Health Network and University of Toronto, Toronto, Ontario, Canada
  1. Correspondence to Professor Runjan Chetty, Department of Anatomical Pathology, Laboratory Medicine Program, University Health Network, Toronto General Hospital, Toronto, ON M5G 2C4, Canada; runjan.chetty{at}


The p16 gene belongs to INK4 family of genes and is made up of four members: p16 INK4A , p15 INK4B , p18 INK4C and p19 INK4D , all of which share biological properties, namely, inhibition of cell growth and tumour suppression. After p53, p16 is the second most common tumour suppressor gene. It has been regarded as the familial melanoma gene. Immunohistochemistry for p16 has a well-defined role in distinct pathological scenarios. It is used to distinguish desmoplastic melanoma from reactive fibrous proliferation, with former showing strong nuclear positivity. In other types of melanoma, p16 protein expression is lost. Spitz nevi show retention of nuclear staining for p16. Benign mesothelial proliferations tend to retain nuclear p16 immunoreactivity, while malignant mesotheliomas lose expression. However, p16 fluorescent in-situ hybridisation analysis is recommended in the workup of malignant mesothelioma. Another common application of p16 immunohistochemistry is as an indicator for human papillomavirus (HPV) infection and p16 protein is overexpressed in HPV-associated tumours. In this context, p16 immunopositivity should be strong, diffuse, nuclear or nuclear and cytoplasmic in location. Another use for p16 is demonstration of p16 immunopositivity in well-differentiated and dedifferentiated liposarcoma.

  • molecular genetics
  • genetics
  • histopathology

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  • Handling editor Cheok Soon Lee.

  • Contributors Both authors contributed equally.

  • Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

  • Competing interests None declared.

  • Patient consent Not required.

  • Provenance and peer review Commissioned; internally peer reviewed.

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