Topoisomerase IIa is a nucleic enzyme that affects the topological structure of DNA and also is a target for chemotherapy (ie, anthracyclines). In this study, we coevaluated its protein expression with chromosome 17 and gene status. Using tissue microarrays, 40 cases of sporadic, primary endometrial adenocarcinomas, 5 cases of atypical hyperplasia, and 5 cases of benign hyperplasia were obtained and reembedded into two paraffin blocks with a core diameter of 1 mm. Immunohistochemistry combined with chromogenic in situ hybridization was performed in 2 and 5 μm sections, respectively. Finally using a semiautomated Image Analysis System, we evaluated the levels of Nuclear labeling index of topoisomerase IIa expression. Statistical analysis was performed by SPSS version 11.0 software. The results indicate that chromosome 17 instability (aneuploidy in 7/40 cases) and Topo IIa gene deregulation (amplification in 3/40 and deletion in 1/40 cases) are significant genetic events correlated with biologic behavior in endometrial adenocarcinoma. Because protein overexpression was observed in a significant proportion of the tumors (18/40), detection of the specific gene deregulation mechanism is a crucial process for application of targeted chemotherapies, which are characterized by different levels of cardiotoxicity and other serious effects.