All IHC stains will include a positive control tissue

Monoclonal antibody targeting the SS18-SSX fusion protein. 

• Reported sensitivity of 87-95% with 100% specificity when strong diffuse nuclear positivity is present (expression in greater than 75% of tumor cells).
• Decreased sensitivity has been reported in decalcified specimens, specimens with delayed tissue fixation, areas of necrosis and in areas of crush artifact.

Prepare a formalin-fixed, paraffin-embedded (FFPE) tissue block

FFPE tissue block

Tissue section mounted on a charged, unstained slide

Ambient (preferred)

• Unlabeled/mislabeled block
• Insufficient tissue
• Slides broken beyond repair

Immunohistochemical staining and microscopic examination

Staining pattern:  Nuclear

The below table from Zaborowski et al highlights an algorithm for the use and interpretation of SS18-SSX.

References:

1. Perret et al. The SS18-SSX antibody has perfect specificity for the SS18-SSX Fusion protein.  Am J Surg Pathol 2021;45(5):582-583.
2. Baranov et al. A novel SS18-SSX fusion-specific antibody for the diagnosis of synovial sarcoma. Am J Surg Pathol 2020;44:922-933.
3. Zaborowski et al. When used together SS18-SSX fusion-specific and SSX C-terminus immunohistochemistry are highly specific and sensitive for the diagnosis of synovial sarcoma and can replace FISH or molecular testing in most cases. Histopathology 2020;77:588-600.