Topoisomerase II alpha 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 alpha is a gyrase involved in cell proliferation, and DNA maintenance and repair. Topoisomerase II alpha is a target of inhibiting agents such as anthracyclines. Triggered by a recent response to topoisomerase II alpha inhibitors in a patient with renal medullary carcinoma, we evaluated topoisomerase II alpha expression in relation to the proliferation index and topoisomerase II alpha 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 alpha 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 alpha over expression. The topoisomerase II alpha gene copy number was evaluated using fluorescence in situ hybridization. Locus specific topoisomerase II alpha gene and chromosome 17 centromere probes were used. The total number of topoisomerase II alpha and chromosome 17 centromere signals was counted in 150 cells per tumor and a topoisomerase II alpha-to-chromosome 17 centromere signal ratio was calculated in each tumor. A topoisomerase II alpha-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 alpha immunohistochemistry was technically inconclusive in 1 renal medullary carcinoma. Topoisomerase II alpha 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 alpha expression in all 13 informative tumors. A strong, statistically significant correlation was found for topoisomerase II alpha and Ki67 expression (pairwise CC 0.9, p = 0.0000). Topoisomerase II alpha over expression was associated with shorter survival (p = 0.000). On fluorescence in situ hybridization no topoisomerase II alpha amplification was detected in any of the 14 renal medullary carcinomas, including the 11 with topoisomerase II alpha over expression. Topoisomerase II alpha 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 alpha is over expressed in 85% of renal medullary carcinomas, potentially supporting the use of topoisomerase II alpha inhibitor agents to treat this aggressive renal tumor. Our findings suggest that topoisomerase II alpha 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 alpha deletions in 28% of renal medullary carcinomas requires further evaluation.