Minichromosome Maintenance
Protein 2 (MCM2) is critical in initiating DNA replication during the cell division process. As expressed intensively in all phases of the active cell cycle, MCM2 has been proposed as a novel
biomarker to determine cellular proliferation. We aimed at clarifying the prevalence and clinical significance of MCM2 in HER2-amplified
breast cancer subtype. MCM2 expression was studied in 142 primary HER2-amplified
breast carcinomas by applying a novel fluoro-chromogenic immunohistochemistry and tailored digital image analysis to determine labelling index (MCM2-LI). The presence of MCM2 was detected with HRP-conjugated
polymer and visualized with 3, 3'-diaminobenzidine tetrahydrochloride, in
cytokeratin (CK)-positive and Cy2-IgG-labelled
breast cancer cells of epithelial origin. Stained slides were digitized by scanning sequentially under bright field (for MCM2) and fluorescence (for CK) illumination. Multilayer JPEG2000 images were analyzed with ImmunoRatio 2.5 (accessory in SlideVantage 1.2 software) utilizing its bright field and fluorescence image-blending mode to display MCM2-CK dual-positive cells. MCM2-LI was retrospectively compared with histopathologic characteristics and patients' clinical outcome. MCM2
protein-expressing cells (median MCM2-LI, 63.5%) were more frequent than those of Ki67 (median Ki67 labelling index, 33%). Significant correlations were found between high MCM2-LI, high Ki67 labelling index, negative
hormone receptor (ER, PR) statuses, high grade of
malignancy, and high
cyclin E expression. MCM2-LI was not shown to be predictive of disease recurrence during the median follow-up of 5.3 years but was shown to be useful to distinguish aggressive-type HER2-amplified
breast carcinomas with high
malignancy grade and
hormone receptor negativity. The fluoro-chromogenic double-labelling immunohistochemistry accompanied with digital image analysis provides an accurate
carcinoma-specific determination of MCM2-LI on a single
tumor section.