Novel characteristics for immunophenotype, FISH pattern and molecular cytogenetics in synovial sarcoma

Area of Science:

• Oncology
• Molecular Pathology
• Cytogenetics

Background:

• Synovial sarcoma (SS) is a rare, aggressive soft tissue sarcoma.
• Its immunophenotype, FISH patterns, and molecular cytogenetics are often poorly understood.
• SS is typically characterized by the t(X;18) translocation.

Purpose of the Study:

• To investigate the immunophenotype, FISH patterns, and molecular cytogenetics of synovial sarcoma.
• To identify diagnostic challenges and confirm SS cases using molecular analysis.
• To characterize novel genetic alterations in SS.

Main Methods:

• Retrospective analysis of morphology using H&E staining.
• Immunohistochemical investigation using SOX-2, PAX-7, NKX3.1, and INI-1 markers.
• Fluorescence in situ hybridization (FISH) for SS18 and EWSR-1 break-apart probes.
• RT-PCR and Sanger sequencing for cytogenetic analysis and fusion gene identification.

Main Results:

• Molecular analysis confirmed SS in 9 out of 13 suspected cases.
• Histological subtypes included monophasic fibrous, biphasic, and poorly differentiated SS.
• Atypical FISH patterns and aberrant EWSR-1 signaling were observed in some cases.
• A novel SS18-SSX1 fusion site was identified in one case, correlating with atypical FISH signals.

Conclusions:

• SS18-SSX fusion gene sequencing is essential for accurate SS diagnosis.
• This is particularly important when encountering confusing immunophenotypes or atypical FISH results.
• Molecular analysis aids in identifying rare genetic variations and confirming challenging SS cases.