Validation of immunohistochemical overexpression of p16 in the histologic diagnosis of cervical intraepithelial neoplasia grade 2.

An accurate cytohistologic diagnosis is important to avoid overtreatment of cervical intraepithelial lesions. The three-tiered Cervical Intraepithelial Neoplasia (CIN) classification, grades 1, 2 and 3, despite poor agreement among pathologists in diagnosing CIN2, is still being used. The College of American Pathologists recommended an alternative two-tiered classification that has not yet been universally accepted. We review the diagnostic results of 286 biopsies performed by three pathologists using haematoxylin and eosin (H&E) and p16 to establish the level of agreement among the readers. Agreement between pathologists in diagnosing CIN2 with H&E was around 45% and improved to 86.7% when interpreting p16 stained biopsies without H&E; agreement with pathologist 3 was lower, around 60%. Discrepant results from one pathologist when assessing p16 highlights the decisive influence of individual criteria. P16 has shown to improve agreement between pathologists with previous good agreement, but did not correct it for the third pathologist. In equivocal cases, protein p16 is a useful conjunctive tool for a histologic diagnosis.