p16^INK4a immunostaining as an alternative to histology review for reliable grading of cervical intraepithelial lesions

Background: Histomorphological grading of cervical intraepithelial neoplasia (CIN) is crucial for clinical management. CIN grading is however subjective and affected by substantial rates of discordance among pathologists, which may lead to overtreatment. To minimise this problem, a histology review of CIN lesions by a consensus panel of pathologists is often used. Diffuse strong p16^INK4a immunostaining has been proposed to aid the identification of true high-grade cervical lesions (ie, CIN2/3). Aim: To assess the value of additional interpretation of p16^INK4a immunostains for making a more reproducible diagnosis of CIN2/3 lesions. Methods: The authors used a series of 406 biopsies of cervical lesions, with known HPV status, stained for both H&E- and p16^INK4a. First, in a randomly selected set of 49 biopsies, we examined the effect of additional interpretation of p16 ^INK4a immunostained slides, on the agreement of CIN diagnosis among three pathologists. Second, the full series of samples was used to assess the accuracy of p16^INK4a-supported lesion grading by a single pathologist, by evaluating the degree of diagnostic agreement with the consensus diagnosis of expert pathologists based on H&E-stained sections only. Results: The study shows that the interobserver agreement between three pathologists for the routine H&E-based diagnosis ranged from fair (weighted kappa 0.44 (95% CI 0.19 to 0.64)) to moderate (weighted kappa 0.66 (95% CI 0.47 to 0.79)). The concordance increased substantially for p16^INK4a- supported grading (mean weighted kappa 0.80 (95% CI 0.66 to 0.89)). Furthermore, an almost perfect agreement was found between the p16^INK4a-supported diagnosis of a single pathologist and the consensus diagnosis of an expert pathology panel (kappa 0.88 (95% CI 0.85 to 0.89)). Conclusions: These data demonstrate that additive use of p16^INK4a immunohistochemistry significantly improves the accuracy of grading CIN lesions by a single pathologist, equalling an expert consensus diagnosis. Hence, the authors advocate the combined use of p16^INK4a-stained slides and conventional H&E sections in routine histopathology to improve accuracy of diagnosis.