Background: Epithelioid sarcoma (ES) is a rare soft tissue neoplasm that usually arises in the distal extremities of young adults, presents a high rate of recurrences and metastases and frequently poses diagnostic dilemmas. In order to identify markers useful for patient stratification purposes, we investigated the prognostic impact of clinical and molecular patient characteristics, including the status of SMARCB1 tumour suppressor gene, in a consecutive series of ES cases.
Methods: Kaplan-Meier survival curves were compared by the log-rank test. Immunophenotyping and SMARCB1 protein expression were analysed by immunohistochemistry or western blotting in 40 ES patients for which tumour material was available. Cases lacking SMARCB1 protein expression were investigated for the presence of gene mutations and gene deletions by exon sequencing, fluorescent in situ hybridization and quantitative PCR.
Results: FNCLCC tumour grade 3 and proximal-type histology significantly correlated with shorter overall survival (log-rank p=0.0046 and p=0.0001, respectively). We identified loss of SMARCB1 protein expression in the majority of ES cases (25/40, 62.5%), including 24/34 (71%) adult cases but only 1/6 (17%) paediatric/adolescent cases (p=0.02, two-tailed Fisher's exact test). The absence of protein is strongly correlated with SMARCB1 gene deletion (p=0.003, two-tailed Fisher's exact test). We observed a trend towards the correlation between SMARCB1 inactivation and both higher tumour grading and a clinical course of the disease characterised by the occurrence of multiple relapses/metastasis.
Conclusion: These data show that both tumour grading and subtype are prognostic factors in ES. Loss of SMARCB1 protein expression in ES is a frequent occurrence mediated by gene deletion events, thus pointing to a crucial role of SMARCB1 in ES genesis. Analysis of SMARCB1 status in ES warrants prospective investigation as a prognostic marker and therapeutic target.
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