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Background: While DNA topoisomerase 2A (TOP2A) plays an essential role in maintaining the structural integrity of the double helix during replication and recombination, excessive expression of this enzyme may promote malignant cell transformations. In fact, increased levels of TOP2A have been observed in various cancer cell lines including squamous cell carcinoma of the lung. This study sought to identify correlations between genotypic and phenotypic evidence of TOP2A obtained via in situ hybridization (ISH) and immunohistochemistry (IHC) techniques.

Methods Tissue microarrays created from 29 samples of Stage I Squamous Cell Carcinoma of the lung were stained with VENTANA BenchMark ULTRA platform with dual color ISH molecular probes TOP2A / CEP17 and antiTOP2A antibody (clone JS5B4-rabbit monoclonal antibody). Gene copy numbers were analyzed using bright field microscopy. Gene amplification was considered in cells exhibiting gene copies > 3 or TOP2A:CEP17 ratios > 1.82. IHC stains were quantified using Spectrum software (Apeiro technologies) using the nuclear algorithm. All levels of protein expression (+1 to +3) were considered positive.

Results: A moderate Pearson Correlation (0.4) between TOP2A gene amplification and protein expression was identified.

Conclusion: While gene amplification moderately correlated with protein expression of TOP2A, additional factors influencing protein expression independently of gene amplification should be identified.

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