The utility of MCM2/TOP2A biomarker in abnormal cervical cytology

Abstract

The introduction of liquid-based cytology (LBC) has contributed to increased detection rates of cervical intra-epithelial lesions due to significant improvement in the sample quality, and its higher sensitivity and specificity when compared to the conventional Papanicolaou test (CPT). To further improve the diagnosis of abnormal cervical cytology and to lower subjectivity and interpretative variability in the evaluation of difficult cytology cases showing atypical cells, the use of cellular biomarkers has been studied and assessed. In this study the diagnostic use of a novel biomarker, MCM2/TOP2A cocktail antibody, for the detection of the overexpression of mini-chromosome maintenance protein 2 (MCM2) and DNA topoisomerase II alpha (TOP2A) proteins in cervical LBC specimens was investigated. One hundred and one cell blocks from residual LBC specimens that were previously diagnosed cytologically as reactive-NILM (negative for intraepithelial lesion or malignancy), low-grade squamous intraepithelial lesion (LSIL), high-grade squamous intraepithelial lesion (HSIL), squamous cell carcinoma (SCC) and atypical squamous cells cannot exclude a HSIL (ASC-H) were prepared and examined. Optimisation processes were performed for the MCM2/TOP2A biomarker to determine the optimal antigen retrieval protocol. The cell block sections were stained with H&E stain to assess cellular adequacy and the chosen cases were subsequently immunostained with the biomarker. The MCM2/TOP2A stained slides were quantitatively and qualitatively assessed by carrying out differential counts and the representative cells were scored by using four different nuclear staining intensity levels. A statistically significant difference was found between the reactive-NILM/LSIL and HSIL/SCC cytology diagnostic categories, which was demonstrated by the stronger immunoexpression in HSIL/SCC cases and weaker staining intensities in reactive-NILM/LSIL cases. When compared with the cytology diagnostic results, the MCM2/TOP2A biomarker yielded a sensitivity of 100% and specificity of 94.3% for the reactive-NILM, LSIL, HSIL and SCC cases. In the correlation between the “gold-standard” histology follow-up diagnosis of ASC-H cases and their respective predicted MCM2/TOP2A results, the sensitivity and specificity of this biomarker were 90% and 93.8% respectively. In conclusion, these results clearly showed the potential utility of MCM2/TOP2A biomarker to be used as an adjunct test to aid in the cytological interpretation and diagnosis of challenging and difficult LBC cases.