Is the expression pattern of BD ProExC the same as Ki-67? A comparative analysis in cervical biopsies

BD ProExC (ProExC) and Ki-67, both used as biomarkers for high-grade cervical intraepithelial neoplasia (HG CIN), yield discordant staining in some cervical biopsies. This study compared ProExC and Ki-67 expression in 197 cervical biopsies with consensus diagnoses (55 negative, 21 atypical squamous metaplasia, 61 low-grade CIN, and 60 HG CIN). Percentages of immunostained nuclei were evaluated by 2 pathologists yielding 68 (35%) cases with discordant ProExC/Ki-67 immunostaining for analysis. In 78% of cases the difference in staining involved <25% of lesional cells. This was noted across all morphologic diagnoses, being most frequent in HG CIN. Discordant staining involving >50% of lesional cells occurred in 22% of discrepant cases, being most frequent in atypical squamous metaplasia. Using staining in >50% of lesional nuclei as a positive result, positive/negative discordance occurred in 25 cases (13% of all cases) including 18% of HG CIN cases. Fourteen cases were ProExC+ (7 of which were strongly p16+) and 11 were Ki-67+ (6 of which were strongly p16+).