Human Papillomavirus (HPV) and p16 Protein

1. HPV and Cancer Risk

• What is HPV? Human papillomavirus (HPV) is a very common virus that can cause conditions such as warts, genital warts, and cervical cancer. HPV is transmitted primarily through skin-to-skin contact, most commonly through sexual contact [1].
• Types of HPV: There are more than 200 types of HPV. Some cause common warts, while approximately 14 types are considered high-risk HPV, particularly HPV 16 and HPV 18. These types can alter cells in the body and lead to cancer [1, 3].
• Not everyone infected with HPV develops cancer: Importantly, HPV infection does not mean that a person will definitely develop cancer. The immune system can often clear the virus within 12 months [1]. However, if the virus persists over a prolonged period, it can cause abnormal cellular changes that may gradually progress to cancer.

2. p16: A Cellular “Warning Signal”

• What is p16? p16 is a naturally occurring protein found in our cells [2]. It plays an important role in regulating the cell cycle, preventing cells from growing too rapidly or abnormally [2].
• p16 is upregulated when high-risk HPV causes cellular changes: When high-risk HPV infects cells and initiates processes that may contribute to malignant transformation, viral proteins such as E7 can inactivate the retinoblastoma protein (pRb), resulting in marked overexpression of p16 [2, 4, 5].
• An important “warning signal”: Increased p16 expression on testing acts as an important signal for physicians, indicating that abnormal cellular changes associated with HPV may be present [2, 6].

3. How Does p16 Help in Cancer Diagnosis?

• In cervical cancer:
  • HPV is the causative agent of virtually all cervical cancers [3].
  • p16 testing can help pathologists better characterize cervical cell abnormalities and identify lesions that may require further evaluation, monitoring, or treatment [2].
• In oropharyngeal cancer:
  • The number of oropharyngeal cancers associated with HPV, particularly HPV-16, has increased in many populations [1, 3].
  • p16 is an important marker for identifying oropharyngeal tumors associated with HPV. In current clinical practice, p16 immunohistochemistry is used as a surrogate marker for HPV-mediated disease in the oropharynx.
  • p16-positive HPV-associated oropharyngeal cancers generally have a more favorable prognosis than HPV-independent tumors and are staged using a separate staging system.

4. Other Cancers Associated With HPV and p16

In addition to cervical and oropharyngeal cancers, HPV and p16 also have roles in several other cancers:

• Anal cancer: HPV is a major cause of anal cancer, and p16 may be used as a diagnostic and disease-assessment marker.
• Vaginal and vulvar cancers: Similarly, high-risk HPV types can contribute to cancers of the vagina and vulva, and p16 can serve as a supportive diagnostic marker.

5. When Will a Doctor Test for p16?

• Abnormal test results: When Pap cytology or HPV testing shows abnormalities suggesting a risk of precancerous lesions or cancer, p16 may help clarify the significance of the findings [2].
• Suspected cancer: When concerning symptoms or findings raise suspicion of cancer in the cervix, oropharynx, or other HPV-associated sites, a biopsy may be performed to establish the diagnosis [1, 2].
• Common p16 testing method: p16 testing is commonly performed using immunohistochemistry (IHC) on tissue biopsy specimens or cell samples [2].

6. Significance of p16 Test Results

• p16-positive result: This indicates increased expression of p16 in the cells examined. It can be a strong indicator of HPV-associated cellular changes, particularly in the appropriate clinical and pathological context, but it does not by itself establish a diagnosis of cancer [2].
• p16-negative result: This indicates that significant p16 overexpression was not detected. Depending on the clinical context, it may reduce the likelihood of an HPV-associated lesion, but the result must be interpreted together with other clinical, cytological, histopathological, and HPV test findings.
• Combining p16 and Ki-67 for more accurate assessment:
  • What is Ki-67? Ki-67 is another cellular protein used as a marker of cell proliferation [7]. Its expression increases when cells are actively dividing.
  • Why use both p16 and Ki-67? Under normal conditions, p16 and Ki-67 are rarely expressed simultaneously in the same cervical epithelial cell. However, when high-risk HPV disrupts the cell cycle and causes high-grade precancerous lesions or cancer, both p16 and Ki-67 may be expressed [7, 8].
  • How do pathologists interpret the results? Pathologists can perform dual staining for p16 and Ki-67 on the same cytology specimen. Detection of a cell that is positive for both p16 and Ki-67 supports the presence of abnormal cell-cycle activity and can help identify patients at increased risk of high-grade cervical lesions (CIN2+) [7, 8, 9]. This combined approach can improve the detection of clinically significant cervical lesions compared with either marker alone [7, 8]. Current cervical screening guidance includes p16/Ki-67 dual-stain testing as a management tool for individuals who test positive for HPV.

7. Benefits of Determining p16 Status in Treatment

• Guiding individualized treatment: Determining p16 status can help physicians better characterize whether an oropharyngeal cancer is HPV-associated. This information can contribute to treatment planning and disease staging, particularly in oropharyngeal cancer, where p16 status is incorporated into the staging system.
• Prognosis and treatment response: Studies have shown that patients with p16-positive, HPV-associated oropharyngeal cancer generally have more favorable outcomes than patients with HPV-independent disease. Therefore, p16 status can provide important prognostic information and contribute to clinical management.

8. Frequently Asked Questions (FAQ)

1. Does a positive p16 result mean that I have cancer?
   • Not necessarily. A positive p16 result is an important indicator of cellular changes associated with HPV, but it is not, by itself, a definitive diagnosis of cancer. Physicians and pathologists interpret the result together with biopsy findings and other relevant clinical information.
2. Is p16 testing painful?
   • p16 testing is usually performed on a tissue or cell specimen obtained from an area of concern. The sample collection may cause mild discomfort or pain depending on the anatomical site and sampling method, while the laboratory analysis of p16 itself is not painful. The physician will explain the specific sampling procedure.
3. How can I find out whether I have an HPV infection?
   • HPV DNA testing can be used to detect HPV infection. For women, HPV testing is commonly used as part of cervical cancer screening. For men or other anatomical sites, testing is performed when clinically indicated.

9. How Can HPV-Related Cancers Be Prevented?

• HPV vaccination: HPV vaccination is an effective way to protect against infection with HPV types that can cause cancer and can help prevent cervical and other HPV-related cancers [1].
• Regular screening: Follow recommended cervical cancer screening schedules, including HPV and Pap testing when appropriate, to detect abnormal cervical changes at an early stage.
• Healthy lifestyle: Avoid smoking and limit alcohol consumption, as these are also risk factors for cancer, particularly head and neck cancers [1, 3].

10. References

• [1] Ferreira, C. C. (2023). The relation between human papillomavirus (HPV) and oropharyngeal cancer: a review. PeerJ.
• [2] Larsen, C. G., et al. (2014). Correlation between human papillomavirus and p16 overexpression in oropharyngeal tumours: a systematic review. British Journal of Cancer.
• [3] Adilbay, D., et al. (2018). HPV infection and P16 expression in oral and oropharyngeal cancer in Kazakhstan. Infectious Agents and Cancer.
• [4] Munger, K. (2013). p16 in HPV-associated cancers. PMC.
• [5] Chung, C. H. (2014). p16 Protein Expression and Human Papillomavirus Status. PMC.
• [6] Sano, T. (1998). Expression Status of p16 Protein Is Associated with Human. PMC.
• [7] Yu, L., et al. (2019). Application of p16/Ki-67 dual-staining cytology in cervical cancers. J Cancer.
• [8] Zhong, P., et al. (2015). P16 and Ki-67 expression improves the diagnostic accuracy of cervical lesions but not predict persistent high risk human papillomavirus infection with CIN1. Int J Clin Exp Pathol.
• [9] Popiel-Kopaczyk, A., et al. (2023). The Expression of Testin, Ki-67 and p16 in Cervical Cancer Diagnostics. Curr Issues Mol Biol.