[700] Topoisomerase IIA Status (TOP2A) in Renal Medullary Carcinoma: Immunoexpression and Gene Copy Alterations of a Potential Target of Therapy

R Albadine, W Wang, NA Brownlee, A Toubaji, A Billis, P Argani, AJ Garvin, GJ Netto. Johns Hopkins, Baltimore; University of Campinas, Brazil; Wake Forest University

Background: Renal medullary carcinoma (RMC) are aggressive neoplasms with no currently available effective therapy. TOP2A is a gyrase involved in cell proliferation, DNA maintenance and repair. TOP2A is a target for agents such as Anthracyclines. Triggered by a recent RMC patient response to TOP2A inhibitors, we decided to evaluate TOP2A expression, in relation to proliferation index, and TOP2A gene copy number status in a larger series of RMC.
Design: Archival tissues from 14 RMC were retrieved from 3 academic institutions. IHC analysis was performed using monoclonal antibodies for TOP2A (Novocastra) and Ki67 (Ventana) . The percentage of positive nuclear staining was assessed in highest area of expression. A previously suggested > 5% cutoff was used for TOP2A overexpression. TOP2A gene copy number was evaluated using FISH. Locus specific TOP2A gene and chromosome 17 centromeres (CEP17) probes (Vysis) were utilized. The total numbers of TOP2A and CEP17 signals were counted in 150 cells per tumor and a TOP2A/CEP17 signals ratio was calculated. A TOP2A/CEP17 ratio 2.0 and <0.8 were used as cutoff for amplification and deletion respectively. Percentages of tumor cells with polysomic, eusomic or monosomic Chromosome 17 status were also determined.
Results: IHC Analysis: TOP2A IHC was technically inconclusive in one RMC. TOP2A was overexpressed in 11/13 (85%) RMC (median 50%, range 1-80%). As expected, a high Ki67 proliferation index was demonstrated in 13/14 tumors (median 87.5%, range 2-100%). Ki-67 was higher than TOP2A expression rate in all 13 informative tumors. Strong statistically significant correlation was found between TOP2A and ki67 expression (pairwise CC=0.9, p 0.0000). FISH Analysis: No TOP2A amplification was detected in any of the 14 RMC including the 11 with TOP2A overexpression. TOP2A gene deletions were encountered in 4 tumors. 2/4 deletions were in association with ch17 monosomy while the remaining 2 deletions were in Ch17 eusomic tumors.
Conclusions: TOP2A is overexpressed in 85% of RMC tumors potentially lending support for TOP2A inhibitors in this aggressive renal tumor. Our findings suggest that TOP2A overexpression in RMC is not due to gene amplification but likely to be due to transcriptional or post transcriptional modifications. The biologic significance of our findings of TOP2A deletions in 28% of RMC requires further evaluation.
Category: Genitourinary (including renal tumors)

Wednesday, March 11, 2009 1:00 PM

Poster Session VI # 105, Wednesday Afternoon