Which expression loss is seen with most pathologic diagnoses of epithelioid sarcoma?

Epithelioid sarcoma is a rare soft tissue sarcoma characterized by distinct pathological features. The consistent finding in most cases of epithelioid sarcoma is the loss of INI1 expression, which is a core subunit of the SWI/SNF chromatin remodeling complex. This complex plays a crucial role in regulating gene expression and maintaining proper cellular function.

The loss of INI1 is significant because it disrupts the normal balance of cell proliferation and differentiation, contributing to tumor development. Pathologists often assess INI1 expression through immunohistochemical staining, and the absence of INI1 is considered a diagnostic criterion for epithelioid sarcoma.

In contrast, loss of the SWI/SNF complex as a whole is less specific, as it encompasses multiple components, not just INI1. Similarly, while EZH2 expression and DNA methylation changes might be relevant in other malignancies, they do not have the same diagnostic value specifically for epithelioid sarcoma as the complete loss of INI1 expression. Therefore, the identification of lost INI1 expression serves as a key marker in the diagnosis and understanding of the pathology of epithelioid sarcoma.