p16INK4a Expression in Cervical Lesions Correlates with Histologic Grading - a Tertiary Level Medical Facility Based Retrospective Study

p16INK4a is a tumor-suppressor protein and cyclin-dependent kinase (cdk) inhibitor that blocks cdk4- and cdk6-mediated pRb phosphorylation to inhibit E2F-dependent transcription and cell-cycle progression. Because the E7 protein of high-risk HPVs inactivates pRB, the resulting overexpression of p16INK4a may be a good marker for infection with high risk HPV types. Immunostaining of p16INK4a allows precise identification of even small CIN or cervical cancer lesions in biopsy sections and can help reduce inter-observer variation in the histopathological interpretation of cervical biopsy specimens. The aims of the present study were to evaluate the expression of p16 INK4a in cervical biopsies and to compare the grade of cervical neoplasia with intensity of staining. The study covered 110 cervical biopsy tissue blocks over a period of 2 years, (85 cases of CIN of varying grade and invasive cervical cancers and 25 of non-neoplastic lesions). Immunostaining with p16INK4a antibodies followed standard operating procedures. The results showed an increasing trend for p16INK4a immunoreactivity from benign to higher grade lesions. Out of 25 cases of non dysplasia (15 cervicitis &10 immature squamous metaplasia), 8%(2/25) showed P16INK4a expression (grade 1). Among low grade lesions like CIN1, 32% (8/25) cases demonstrated P16INK4a expression (grade 1). Some 52.3% (11/21) of CIN2 cases proved positive. The intensity of p16INK4a expression in CIN 2 was grade 1 in 33%, grade 2 in 14% and grade 3 in 4.7% of cases. All the CIN3 lesions and cervical squamous cell carcinomas exhibited grade 3 anti p16INK4a antibody staining. The association of p16INK4a expression with histologic grade of cervical pathology was highly significant (χ2-value:51.81, p<0.0001). The staining intensity increase with higher grade disease was also statistically significant (χ2-value :133.95, p<0.0001).