ERG and FLI1 protein expression in epithelioid sarcoma.

Area of Science:

• Oncology
• Pathology
• Molecular Biology

Background:

• Epithelioid sarcoma is a rare, aggressive sarcoma.
• It can express keratin and CD34, and may be misdiagnosed as angiosarcoma.
• ERG, a marker for vascular differentiation, has been observed in epithelioid sarcoma.

Purpose of the Study:

• To investigate the prevalence of nuclear expression of ERG and FLI1 in epithelioid sarcoma.
• To compare ERG and FLI1 expression with vascular markers (CD34, CD31, D2-40).
• To assess the utility of different ERG antibody epitopes (N-terminus vs. C-terminus) in diagnosing epithelioid sarcoma.

Main Methods:

• Tissue microarray of 37 epithelioid sarcomas.
• Immunohistochemistry for ERG (N- and C-terminus), FLI1, CD34, CD31, and D2-40.
• Grading of immunoreactivity based on percentage of positive tumor cell nuclei and staining intensity.

Main Results:

• Nuclear staining for ERG N-terminus observed in 19/28 cases, with 10 showing diffuse, strong/moderate labeling.
• Focal ERG C-terminus staining seen in only 1/29 cases.
• FLI1 labeling detected in 28/30 cases, often with diffuse, moderate to weak staining. CD34 positive in 22/30, D2-40 in 22/31, and CD31 negative in all cases.

Conclusions:

• Epithelioid sarcoma can express ERG (N-terminus) and FLI1, potentially leading to misdiagnosis as a vascular tumor.
• ERG antibody selection is critical; N-terminus antibodies are more likely to label epithelioid sarcoma than C-terminus antibodies.
• A diagnostic panel including SMARCB1 and CD31 is recommended for evaluating epithelioid sarcoma.