Topoisomerase II α Status in Renal Medullary Carcinoma: Immuno-Expression and Gene Copy Alterations of a Potential Target of Therapy

Purpose

Renal medullary carcinoma is an aggressive renal neoplasm without currently available effective therapy to our knowledge. Topoisomerase II α is a gyrase involved in cell proliferation, and DNA maintenance and repair. Topoisomerase II α is a target of inhibiting agents such as anthracyclines. Triggered by a recent response to topoisomerase II α inhibitors in a patient with renal medullary carcinoma, we evaluated topoisomerase II α expression in relation to the proliferation index and topoisomerase II α gene copy number status in a larger series of patients with renal medullary carcinoma.

Materials and Methods

Archival tissues from 14 renal medullary carcinomas were retrieved from our 3 institutions. Immunohistochemistry was performed using monoclonal antibodies for topoisomerase II α and Ki67. The percent of cells with positive nuclear staining was assessed in the highest area of expression for each marker. A previously suggested greater than 5% cutoff was used for topoisomerase II α over expression. The topoisomerase II α gene copy number was evaluated using fluorescence in situ hybridization. Locus specific topoisomerase II α gene and chromosome 17 centromere probes were used. The total number of topoisomerase II α and chromosome 17 centromere signals was counted in 150 cells per tumor and a topoisomerase II α-to-chromosome 17 centromere signal ratio was calculated in each tumor. A topoisomerase II α-to-chromosome 17 centromere ratio of 2.0 or greater and less than 0.8 was used as a cutoff for amplification and deletion, respectively. The percent of tumor cells with polysomic, eusomic or monosomic chromosome 17 status was also determined.

Results

On immuno-expression analysis topoisomerase II α immunohistochemistry was technically inconclusive in 1 renal medullary carcinoma. Topoisomerase II α was over expressed in 11 of 13 renal medullary carcinomas (85%) (median 50%, range 1% to 80%). As expected, a high Ki67 proliferation index was noted in 13 of 14 tumors (median 87.5%, range 2% to 100%). Ki67 expression was greater than topoisomerase II α expression in all 13 informative tumors. A strong, statistically significant correlation was found for topoisomerase II α and Ki67 expression (pairwise CC 0.9, p = 0.0000). Topoisomerase II α over expression was associated with shorter survival (p = 0.000). On fluorescence in situ hybridization no topoisomerase II α amplification was detected in any of the 14 renal medullary carcinomas, including the 11 with topoisomerase II α over expression. Topoisomerase II α gene deletions were noted in 4 tumors. Two of 4 deletions were associated with chromosome 17 monosomy and 2 were in eusomic chromosome 17 tumors.

Conclusions

Topoisomerase II α is over expressed in 85% of renal medullary carcinomas, potentially supporting the use of topoisomerase II α inhibitor agents to treat this aggressive renal tumor. Our findings suggest that topoisomerase II α over expression in our renal medullary carcinoma cohort was not due to gene amplification, but rather to transcriptional or post-transcriptional modifications. The significance of the incidentally found topoisomerase II α deletions in 28% of renal medullary carcinomas requires further evaluation.

Key Words: kidney, carcinoma, kidney medulla, DNA topoisomerase II alpha, gene deletion

Abbreviations and Acronyms: CEP17, Ch17 centromere, Ch17, chromosome 17, FISH, fluorescence in situ hybridization, IHC, immunohistochemistry, RMC, renal medullary carcinoma, TOP2A, topoisomerase II α