Expression of P16INK4A Protein in Cervical Intraepithelial Neoplasia and Invasive Carcinoma of Uterine Cervix

Introduction: Cervical cancer still ranks as the most frequent cancer among women in India. Infection with Human Papilloma Virus (HPV) results in precancerous lesions and invasive cervical cancer. Interaction of HPV oncogenic proteins with cellular regulatory proteins leads to upregulation of p16INK4A, a cyclin dependent kinase inhibitor. Therefore, p16INK4A overexpression is a surrogate biomarker of HPV infection making it useful in evaluating HPV associated premalignant and malignant lesions of gynaecological tract.

Aim: This study was conducted to evaluate the usefulness of p16INK4A as a biomarker in dysplastic and malignant alteration of cervical epithelium. A total of 57 specimens diagnosed histopathologically as cervical dysplasia or malignancy were included in this prospective study of two year duration. Immunohistochemical (IHC) study of p16INK4A expression was performed on normal cervical tissue samples, Cervical Intraepithelial Neoplasia (CIN) 1, CIN 2, CIN 3, squamous cell carcinoma, adenocarcinoma. Expression was scored by two methods. One was simple positive versus negative p16INK4A staining and the other method was a semi-quantitative IHC scoring (0 to 8 points) according to the intensity of staining and the proportion of stained cells. The collected data was entered in excel sheet and analysed using Statistical Package For Social Science (SPSS) 16.0 software and the descriptive statistics, Chi-square test. The p-value of <0.05 was considered statistically significant.

Results: Nuclear and/or cytoplasmic p16INK4A immunoreactivity was absent in normal cervical tissue, while immunopositivity was 25% in CIN 1, 50% in CIN 2, 75% in CIN 3, 75% and 100% in squamous cell carcinoma and adenocarcinoma respectively. All normal cervical samples had low scores (0 to 2 points), while number of cases with high scores was proportional to the degree of cervical dysplasia or invasive carcinoma. p16INK4A immunostaining with higher expression (score>5) was observed in 75% cases of carcinoma cervix.

Conclusion: IHC expression of p16INK4A is related to degree of histological dysplasia and malignancy, suggesting its prognostic and predictive value in the management of cervical cancers.