Immunohistochemical expression of p16INK4a and bcl-2 according to HPV type and to the progression of cervical squamous intraepithelial lesions

Inactivation of the cell cycle inhibitor gene p16MTS1 seems to be involved in human papillomavirus(HPV)-related carcinogenesis because E6 and E7 oncoproteins may impair p16(INK4a) and, indirectly, bcl-2 functions. In this study, we analyzed the role of immunohistochemical expression of p16(INK4a) and bcl-2 in HPV-infected cervical biopsies as prognostic markers of the progression of squamous intraepithelial lesion (SIL). Sixty-five cervical biopsies were stratified into two subgroups according to the second biopsy: 27 of them maintained a low-grade (LG)-SIL diagnosis, and 38 progressed from LG-SIL to high-grade (HG)-SIL. P16(INK4a) and bcl-2 quantitative expression levels were measured by the immuno-peroxidase method. PCR-DNA techniques were used to detect and type HPV. The Wilcoxon and Fisher exact tests were employed for the statistical analysis. In the group with an LG-SIL diagnosis at the second biopsy, no significant associations were found between p16(INK4a) and bcl-2 expression and presence of HPV16/18. In the group that progressed to HG-SIL, a significant association was observed between p16(INK4a) overexpression and HPV16/18 presence (p=0.021), but none with bcl-2 levels. It is concluded that immunohistochemical bcl-2 expression may not be useful for predicting the progression of HPV-related SIL. In contrast, p16(INK4a) overexpression seemed to be associated with HPV 16 and 18, suggesting that it may be a good marker for predicting SIL progression.