SWI/SNF Chromatin-remodeling Complex Status in SMARCB1/INI1-preserved Epithelioid Sarcoma

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The SWI/SNF chromatin-remodeling complex, which is composed of evolutionarily conserved core subunits such as SMARCB1/INI1 (INI1), SMARCA4/BRG1 (BRG1), SMARCC1/BAF155 (BAF155), and SMARCC2/BAF170 (BAF170), can be viewed as the prototype of an epigenetic regulator of gene expression that is involved in tumor suppression. Epithelioid sarcoma, which classified as a tumor of uncertain differentiation, shows an almost complete loss of INI1. However, some cases of epithelioid sarcoma have preserved INI1, and the clinicopathologic features of these cases are uncertain. To date, there has been no investigation focused on the SWI/SNF chromatin-remodeling complex in INI1-preserved epithelioid sarcoma cases. First, an investigation of INI1 immunoexpression statuses in 60 formalin-fixed paraffin-embedded epithelioid sarcoma specimens (proximal type, 29 cases; conventional type, 31 cases) was performed. In the available INI1-preserved epithelioid sarcoma cases, we analyzed the BRG1, BAF155, and BAF170 protein expressions. INI1 preservation was observed in 6 of 29 (21%) proximal-type and 2 of 31 (6%) conventional-type epithelioid sarcoma cases. Six cases of INI1-preserved epithelioid sarcomas of proximal type were available for further immunohistochemical study. One proximal type showed loss of BAF170, and 2 proximal-type cases revealed loss of BRG1 with preservation of the other remaining core subunit proteins. One proximal-type case showed a mosaic pattern of BRG1 and loss of BAF155. However, in the remaining 2 proximal-type cases, all core subunit proteins were preserved. Overall, these results suggest that loss of expression of SWI/SNF chromatin-remodeling complex proteins has an important role in tumorigenesis. The remaining 2 INI1-preserved epithelioid sarcoma cases may have had other abnormalities causing dysfunction of SWI/SNF chromatin remodeling.

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