Introduction
P16ink4a IHC marker is a surrogate marker for HPV infection and the expression of P16ink4a in association with HPV-High risk infection has been observed.1, 2, 3 HPV associated tumors have been credited with a better clinical outcome and favorable prognosis.1, 2 Hence, HPV detection in Oral squamous cell carcinoma gains importance.
It has been observed that the cases of oropharyngeal carcinoma associated with active HPV-DNA may need deintensified regimens, which reduces the long term negative impact of treatment. Such cases may be singled out by IHC detection of P16ink4a.3
The early oncogenes of HPV mainly E6 and E7 play a key role in carcinogenesis through inactivation of p53 and retinoblastoma(pRb).1, 4, 5, 6 E7-E2F complex effectively stops the negative feedback action of pRb on p16, there by resulting in over-expression of p16. 1, 7, 4 This causes deregulation of cell cycle, thus facilitating DNA damage leading to cellular transformation.
Further, it has been observed that P16ink4a is a strong independent prognostic indicator.7, 3 It also shows high sensitivity and specificity towards HPV detection. Oral cancers have multiple etiological factors and the major contributing factors include tobacco and alcohol intake. 7
Aims and Objectives
The present study was aimed to assess the immunohistochemical expression of p16 in oral lesions such as high grade dysplasia, squamous papilloma and oral squamous cell carcinoma, epitheliomatous hyperplasia and irritable fibroma.
To correlate the patterns of P16 expression with respect to different grades of oral squamous cell carcinomas.
Materials and Methods
Formalin fixed paraffin embedded (FFPE) tissue blocks of 29 histologically proven cases of oral lesions, including normal mucosa as a control. The cases were retrieved from the archives of Department of pathology. Clinicopathological data of all cases were taken from the patient records and tabulated. The study was carried out after approval of the Institutional Ethics Committee.
Tissue sections of 4 µm were obtained on silane coated slides and subjected to IHC staining. Immunohistochemical analysis with anti-human P16ink4a was performed on the serial sections. The panel used was clone MX007. The procedure provided by the manufacturer was followed for staining. Brown precipitate in the nucleus/cytoplasm/both were considered to be a positive p16 expression.
Parameters such as percentage positivity, pattern of expression, intensity and layers of epithelium showing positive staining were assessed. Number of positive cells (x) in an evenly stained area under 40x magnification was counted in each slide. The intensity was scored as absent, mild or intense.
Results
Table 1
Distribution of cases
Table 2
Comparison of IHC expression of p16 among groups
|
Parameters |
No. of cases |
|
% Positivity |
|
|
0-30% |
15 |
|
31-60% |
5 |
|
61-90% |
8 |
|
>90% |
1 |
|
Pattern |
|
|
Nuclear |
3 |
|
Cytoplasm |
5 |
|
Both |
10 |
|
Negative |
11 |
|
Intensity |
|
|
Mild |
17 |
|
Dense |
1 |
The result was found mainly at the basal, parabasal cells and sometimes entire epithelium. The reaction was also identified in normal fibroblasts, glandular acini and endothelial cells.
No correlation was seen between the expression of P16 and localization of the lesion, age, gender or grading.
Figure 7
435/19, scanner view focal strong positivity of P16 in well differentiated squamous cell carcinoma, Tongue
Figure 8
1300/17, SCANNER VIEW Diffuse strong positive P16 ink4a marker in squamous cell carcinoma grade 2, tongue
Discussion
The etiology of oral cancers is multifactorial and a sequential process. Highest incidence of oral squamous cell cancers is also associated with the habit of reverse smoking, and chewing tobacco. Several factors involving oral carcinogenesis are age, gender, lifestyle, genetic background and status of health.2
The prognosis of P16ink4a marker has been reported to be better, irrespective of histologic grade. However, it was observed that no single pattern of expression was strongly associated with the marker. As we have not linked with HPV DNA analysis in the oral lesions, it is not possible for us to comment on the association of HPV in Oral SCC.
Table 3
Correlation with other studies
Conclusion
The present study demonstrates the importance of over-expression of P16ink4a marker in oral squamous lesions.
P16ink4a immunohistochemical marker can be used as a surrogate biomarker for HPV detection of oral epithelial dysplasia’s and oral squamous cell carcinomas.
However, HPV DNA detection is required to validate the utility of IHC detection of P16ink4a as a surrogate marker for HPV association.
