BD ProEx C: a sensitive and specific marker of HPV-associated squamous lesions of the cervix

BD ProEx C (ProEx C) is a recently developed immunocytochemical assay that targets the expression of topoisomerase II-alpha and minichromosome maintenance protein-2, 2 genes shown to be overexpressed in cervical cancers. Recent studies validated this reagent in liquid-based cytology specimens and suggested its usefulness as an adjunct in the diagnosis of challenging cases. Limited information is available on its expression in tissue sections. This study aims to assess ProEx C expression patterns in benign, atypical, and dysplastic lesions of the cervix and to compare these patterns with p16 and Ki67 expression and with the presence of human papilloma virus DNA as determined by in situ hybridization. ProEx C positivity was limited to the basal layers of the epithelium in 75% of benign cervices. In the remaining 25%, staining extended into the lower half of the epithelium particularly in areas of squamous metaplasia and immature squamous metaplasia. In 92% of high-grade dysplasias [cervical intraepithelial neoplasia (CIN) II and III] strong positive staining for ProEx C involved the lower and upper halves of the epithelium. Condylomas and CIN I showed greater variability in staining pattern with ProEx C positivity extending into the upper half of the epithelium in 48% of cases. Statistically significant correlations were noted with presence of human papilloma virus DNA and with p16/Ki67 expression. Atypical squamous metaplasia showed varied staining with 24% being positive. To summarize, ProEx C is a reliable marker for high-grade CIN that can be applied to tissue sections to confirm the diagnosis of high-grade CIN and to triage cases of atypical squamous metaplasia. ProEx C may also have a potential role in triaging patients with low-grade CIN. ProEx C expression patterns are similar to those for p16 and Ki67 with most discrepancies occurring in the CIN I category.