Evaluation of topoisomerase IIa expression in pancreatic ductal adenocarcinoma: a pilot study using chromogenic in situ hybridization and immunohistochemistry on tissue microarrays.

Background/aims: To co-evaluate topoisomerase IIa (Topo IIa) protein expression and gene status in pancreatic ductal adenocarcinoma, determining the potential prognostic impact of its alterations.

Methods: Using tissue microarrays, 50 sporadic, primary pancreatic ductal adenocarcinomas were cored twice and re-embedded into one paraffin block with a core diameter of 1 mm. Immunohistochemistry and chromogenic in situ hybridization were performed in serial tissue sections for the detection of protein expression levels, chromosome 17 and Topo IIa gene status, respectively. Finally using a semi-automated image analysis system we evaluated the levels of protein expression.

Results: A significant proportion of the tumors showed Topo IIa overexpression (32/50 or 64%). Gene amplification and deletion were detected in 9 and 4 cases, respectively, associated with protein overexpression. Aneuploidy regarding chromosome 17 was observed in 19/50 tumors and correlated with poor survival rate (Cox regression test: p = 0.001). Topo IIa protein expression was strongly correlated with stage (p = 0.021) and grade (p = 0.034).

Conclusions: Topo IIa gene amplification correlates with protein overexpression, but not vice versa. This is a crucial observation for the application of targeted chemotherapies, such as anthracyclines, only in subgroups of patients, according to molecular deregulation criteria and not only to immunohistochemical results. Also, chromosome 17 and not Topo IIa gene instability can be used as a potential independent prognostic factor.